Ludwig Prandtl
A Biographical Sketch, Remembrances and Documents

German original by

Johanna Vogel-Prandtl
English translation by

V. Vasanta Ram
Published by
The International Centre for Theoretical Physics
Trieste, Italyon the occasion of the 100th anniversary of the publication in 1904of Prantdl’s paper on the boundary layer theory
August 14, 2004

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Ludwig Prandtl
4.2.1875 − 15.8.1953

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A few words about the translation
Ever since I received from Professor Ernst Mueller, now more than ten years ago, a copyof Ludwig Prandtl’s biography, authored in German by his daughter Mrs. Johanna VogelPrandtl, I wanted to have the text translated to English. Prandtl was clearly one of thegreatest fluid dynamicists ever, but his later life seemed to me to be somewhat tragic forreasons that the readers will soon see. I was especially keen that the contents of Prandtl’s
letter of 1941 to Hermann Goering, decrying the outbursts against “Jewish Science”,
which had evolved into a political movement in Nazi Germany, should be made public. It
must have taken some courage and concern on Prandtl’s part to note that “they [theantagonists of “Jewish Physics”] have poisoned the air with ... disdain for the past...” Seealso Chapter 21 of this book. This aspect of Prandtl's personality was counter to thenotion that was in circulation after the second world-war---that he was a naïve man who
had buried his head in the sand. I immediately made some inquiries for translation andpublication of the book but the project stalled for a number of reasons, including
finances. Both Ernst Mueller and the biographer, with whom he was in contact about thepossibility of the translation, passed away sometime thereafter, which slowed the projecteven further.
The occasion of the 100th anniversary of Prandtl’s 1904 paper on boundary layers
revived the idea in my mind and I was fortunate that Dr. V. Vasanta Ram readily agreed
to translate the biography. For him, as for me, it has been a labor of love. As one ofProfessor Hermann Schlichting’s Ph.D. students, Vasanta Ram belongs to Prandtl's
academic family, is knowledgeable about both German and English, and thus an ideal
person to have undertaken the task. He has worked hard on the translation despite his
physical handicap and other hurdles that he and I faced during the exercise. He
commands my unstinted praise and gratitude. I also wish to thank Professor Roddam
Narasimha for being a steady source of encouragement.
It is my hope to be able to soon place the translation as a book published by aninternational publisher. This version is complete but various improvements are possible.
It seemed important to use the occasion of the IUTAM meeting to distribute the material
in the present form on the CD that you currently have in your possession. I hope that you
will find its reading as much of an occasion as I did for reflecting on the vicissitudes oflife.
One obvious aspect requires specific mention: the author of the German original was not
a professionally trained scientific biographer. This book is thus an intimate account of theperson she loved and admired. The translator has kept alive the same informal spirit andstyle everywhere. I have reviewed the translation numerous times but none of mymodifications has attempted to alter this feature.
Katepalli R. Sreenivasan
Trieste, 21 July 20043

Author's foreword by Johanna Vogel-Prandtl
Translator’s preface by V. Vasanta Ram
Chapter 1. Introduction
Chapter 2. Childhood
Chapter 3. As a student, and an employee at MAN
Chapter 4. Engagement and marriage
Chapter 5. 1911-1918, daily routine
Chapter 6. A day at home
Chapter 7. Gliding
Chapter 8. 'Call' to Munich
Chapter 9. Building up of the Institute and new projects
Chapter 10. The new Kaiser-Wilhelm-Institut
Chapter 11. Journey to London
Chapter 12. Journey to Japan
Chapter 13. A day at home again
Chapter 14. Journeys on vacation
Chapter 15. The year 1933
Chapter 16. Honorary doctorates at Cambridge and Trondheim
Chapter 17. The house in the mountains
Chapter 18. Pleading for W. Heisenberg
Chapter 19. Voices on the situation at that time
Chapter 20. Congress in America
Chapter 21. Physicists' dispute
Chapter 22. Journey to Romania
Chapter 23. The last war years
Chapter 24. The end of the war
Chapter 25. New beginning at the university
Chapter 26. The first post-war years
Chapter 27. The last years of life
Chapter 28. Concluding remarks
Appendix
Literature cited
Glossary4

Author's foreword
By Johanna Vogel-Prandtl
In the course of the last few years, I have felt more and more impelled to sketch abiographical study of the personality of my father, Ludwig Prandtl. As his daughter, I
could, after all, use many personal memories as a basis for preparing a sketch that would
do justice to the different facets of his personality. Scenes that took place within the
innermost circle of the family should not be absent from such a sketch---scenes
reflecting Prandtl's nature that I, as the last member of his family, would like to put onrecord, at least for the sake of my children and of those who knew Prandtl either
personally or by name.
I must mention that my uncle, Professor Ludwig Föppl, brought up the subject of writing
memoirs again and again in conversations with his brother-in-law, trying to impress on
him the importance of doing it on reaching the age he had, just as his father August Föppl
had done earlier. Prandtl always put him off, saying with a smile: ''Probably later, I still
have many other important things to do!'' But I knew Father well enough to realize that
he had no intention whatever of reflecting upon his own life and writing about it, then orlater.
When Father died in 1953, my uncle, Ludwig Föppl, approached me saying: ''Now you
should write about him!''
In any case, this first suggestion set me thinking on how I could possibly succeed in suchan undertaking. One shortcoming would certainly not escape notice. I would certainly not
be in a position to give professionally competent interpretations of his scientific work,and could therefore speak only in very general terms on it. But his scientific output has
been extensively documented in his Collected Works (Gesammelte Abhandlungen [50]),
and this is accessible to the reader. Besides, there are numerous further references given,
which facilitate the interested reader in continuing his or her study of Ludwig Prandtl's
work.
When I finally began sorting out papers to write this biography, it turned out that I could
fall back on many published material in these matters that had appeared in journals,
articles and letters. These are often quoted here. It is quite possible that aerodynamicists
and readers interested in science would find my commentaries on particular works ofPrandtl inadequate. My objective here has only been to make at least a reference to all thework that obviously occupied such a central position in his life.
My more important purpose in this book, however, is to describe the ''human being'' inLudwig Prandtl. This venture owes much to his letters and articles, and to letters by his
pupils, so that my account can for the most part claim a certain authenticity.
Finally I wish to thank my husband for going through the text and for making corrections.

5Special thanks are due to Herr Dr. Julius Rotta, whose close participation in my work
made him contribute several supplements. He added scientific articles to the book andexamined many quotations for their authenticity. The extensive bibliography of Ludwig
Prandtl's writings, prepared by him, has added special value to this book. I wish to extend
particular thanks to Herr Dr. Julius Rotta also for proof-reading the work.
I feel I owe a debt of thanks also to Herr Dr. Walter Tillmann, the administrator of the
MPI-Archives, for his obliging help and competent assistance at the stage of the bookgoing into print.

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Translator's preface
By V. Vasanta Ram
It is perhaps no exaggeration to state that it is unlikely to find a fluid dynamicist today
who is not in some way influenced by works of Prandtl, of which his 1904 paper onboundary layers is seminal. The Translator is no exception. Later, when he was a research
student at Prof. Schlichting's Institut für Strömungsmechanik in Braunschweig, he had theoccasion to come in contact with people who had worked with Prandtl. During this period
and later, he obtained glimpses of Prandtl's personality through occasional and informal
narratives of people who knew him in person. These accounts, together with what theTranslator had read about Prandtl in published literature, generated in him a keen interestin wishing to learn more about Prandtl's personality. This interest remained unfulfilled fora long time, until Johanna Vogel-Prandtl's biographical sketch of her father, "Ludwig
Prandtl---Ein Lebensbild, Erinnerungen, Dokumente", appeared as a report of MPI in
1993, in German. This publication, while meeting the immediate needs of the present
Translator, made him feel that its contents ought to be made known to the community of
fluid dynamicists in the world as a whole, many of whom today may not be conversant
with German. This feeling would have, most probably, merely stayed as an intention
within the Translator's person, had his long-standing friend, Professor K.R. Sreenivasan,
not given him the impetus for undertaking the translation into English. The Translator
then consulted Dr. J.C. Rotta on his thinking about this proposal. Dr. Rotta had worked
with Prandtl and his assistance in the preparation of the biography had been
acknowledged by its author. Dr. Rotta warmly welcomed the proposal and introduced theTranslator to Herr Vogel, with recommendations. Herr Vogel was very receptive to theidea. The response on the whole was encouraging to the Translator to undertake the task,
and the result is the document that is in your hands presently.
Early during the course of the translation, it became clear that, in order to preserve thespirit of the original, it would be necessary to take over many German words unchanged
into English. Some of the reasons are the following:Firstly, the differences between the way research work is organized and conducted inGerman universities---with the Instituts headed by an Ordinarius who is provided with
Assistents and other Mitarbeiter---and in universities in the English-speaking world, areindeed very wide. Therefore, there is often no counterpart to certain positions in theGerman set-up. Literal translation of the designations would be misleading, so theTranslator has opted to keep the German word unchanged.
Secondly, the Translator regards it as a sign of respect for the other culture that theirproper names, in particular of their towns and cities, should be written as closely as
possible to the pronunciation in the other tongue. So the city of Hannover is spelt with adouble-n, and the city where Prandtl was first employed as Nürnberg, instead of as'Nurenberg'. An exception, however, is made in writing Munich instead of München,since the former has firmly established itself in all English-speaking countries.

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Thirdly, when following an established course in translating a certain word, a distortionof meaning could occur. A particularly outstanding example for such a distortion is when
the word arisch is translated as 'aryan', although this is found to be common in manytranslations. In short, the NAZI use of the word arisch is almost exactly opposite to themeaning of the word 'aryan' (see Glossary). Therefore, the Translator has kept the wordarisch unchanged to convey the meaning assigned by the NAZIs in their context.
German words taken over unchanged in the translation have been denoted in italics. They
have been put together in the Glossary at the end, which, although incomplete, attempts
to provide a brief explanation of the terms.
The Translator prepared a draft of the translation and sent the same to Herr Vogel for hiscomments, who then suggested improvements in the draft. Some of these changes havealready been made in the current version, but there has not been sufficient time toincorporate all of them. It is hoped that it will be possible to do this soon. The draft, after
making these corrections, was sent in an electronically readable form to Professor K. R.
Sreenivasan, who has personally attended to the work of lay-out and editing.
First and foremost, thanks are due to Herr Vogel and to Dr. Rotta for their encouragement
and support to the Translator to undertake this work.
The Translator owes a deep debt of gratitude to Mr. Arun Prasad, Professor Roddam
Narasimha and Professor K.R. Sreenivasan, who went through the draft in detail, pointed
out to the shortcomings of an earlier version, and suggested improvements. Without theiractive support, the translation would not have reached its present stage.
The Translator wishes his work to be regarded as a sign of his thanks to the culture thathas nurtured him for so many years, although he comes from an entirely different
background. He would also see its purpose fulfilled if his translation contributes towards
mutual understanding of cultures, which, he believes, is more the need of the hour thanever before. This outlook is a product of his experiences in life taken as a whole, andreflects a certain philosophy that has evolved therefrom. Although it is hard to trace with
precision the origin of a particular trait of this Weltanschauung, some personalities, withwhom the Translator had constantly been in touch---in person, through correspondence,and through their literary/scientific/other works---have left an indelible impression on
him. He wishes to acknowledge the support he enjoyed of these personalities:
Masti Venkatesa Iyengar, author of literary works in the (South-) Indian language,
Kannada, and in English, India;
Prof. Hermann Schlichting, Germany;
Prof. Joseph Kestin, USA;
Prof. Keith Stewartson, UK;
Prof. Itiro Tani, Japan; andHephzibah Menuhin and Lord Yehudi Menuhin, UK

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1. Introduction
What memories do I have of my father? His benevolent nature and inner harmony arestill present with me just as his calm and thoughtful manner, which was wholly
undeterred by the mostly impatient fervor of his surroundings. I see him in front of myeyes, customarily handling things around him with care. When he raised the weight towind up the wall-clock, which was, by the way, always well regulated, he did so with his
hand supporting the weight and paused for a moment to listen attentively to the regularbeat of the pendulum before gently closing the glass door of the clock.
He had a very pronounced liking for keeping and preserving things. Our simple style oflife at home remained unchanged over the years. At home, the attention to utilitarianconsiderations took precedence over modernization. The force of this habit dictated what
existed to continue almost without any change. I really do not remember my father everexpressing any material desires. In fact, his tremendous modesty and simplicity enabledhim, in fact, to be grateful and contented with small gifts during the post-war years ofsevere hardship.
He would have been surprised if he came to know of my aspirations to put the past on
record, and he would have probably objected by saying that his life, of which I am
writing now, had not been very important.

92. Childhood
Unfortunately, that my attempt now to narrate my father's childhood can only befragmentary, by giving a disjointed account since there is none left who could havehelped me unearth all the memories. I will therefore be content with relating details that I
have partly taken from my grandfather's mnemonic notes, in which he faithfully, eventhough only sketchily, recorded the development of his only son, and from stories ourfather told us from his memory. I have taken out the facts about the family history fromthe genealogical records gathered together by two cousins of my father, Professor
Wilhelm Prandtl and Ministerialrat Carl Prandtl.
Ludwig, the first child of Alexander Prandtl, Professor at the Weihenstephan Agricultural
College near the town of Freising, and his wife Magdalena (nee Ostermann), was born on
Thursday 4 February 1875 at quarter to seven in the evening on the third floor of thehouse of his widowed grandmother Maria Ostermann, whose husband was a merchant byprofession.
At that time, the house of his birth in Freising, at Hauptstrasse 64, was in the possessionof the Ostermann family for over one hundred years. The founder of the family was
Ludwig Ostermann who had moved in from Austria to settle there in 1760. Together withhis brother Franz, who was working as a glass painter, he had left his hometown
Kranebitten near Kiefersfelden to build up a new existence in Freising. Their newly
founded grocer's shop was adjacent to one of the city gates known as ''Veitstor''.
However, this gate had to be pulled down in 1875 due to its dilapidated state, which inturn required some changes to be made in the house of the merchant, too. To the west of
the house, there were horse stables and flat cots that belonged to a pub. The rear windows
allowed a view on medieval gables and small back-yard houses.
In 1869, when he took up his position as a professor at the Weihenstephan Central Schoolof Agriculture in Freising at the age of 29, Alexander Prandtl rented a room in themerchant's house from the widow Maria Ostermann. He came there from Munich where
he had completed his studies at school and university. After attending the Munich
Polytechnical School, from which he had graduated as a Kulturingenieur (CulturalEngineer) and assumed a position of a civil servant in Lower Bavaria. He had now beencalled to take up the position of a Professor of Applied Mathematics and Soil
Improvement/Melioration (Meliorationskunde). The following subjects were also taught
at Weihenstephan: agricultural chemistry, drawing of agricultural implements and plants,
anatomy and physiology of domestic animals, forestry, meteorology and others. The
associated brewery served for practical training. Alexander was working there as ascientist in the laboratory of the experimental dairy station. From 1870 to 1875, heprimarily worked on the design of a continuously operating milk centrifuge. The idea todeal with the problem of fat extraction from milk through the centrifugal force came fromhis brother Antonin, who had written a paper on this subject in the Polytechnical Journal
eleven years ago, approaching the practical task of increasing the concentration of milk
from a chemical point of view. Alexander succeeded in making substantial improvements
to his brother's design, and showed his new fat extraction machine at the 1875 World

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Exhibition in Frankfurt on the Main. The world's first continuously operating milk
centrifuge attracted considerable attention as an exhibit and provided inspiration forfurther development. Later on, the same model was exhibited in the Dairy Division of theDeutsche Museum (in Munich). In the following years, he developed a new machine, amilk separator that enabled the milk to be separated into its individual components
without getting creamed. Alexander also published several scientific/technical articles in
the Weihenstephaner Milchzeitung (Weihenstephan Milk Journal) which I want to list
here for the sake of completeness. An article from 1877 was "Über den theoretisch zu
erwartenden Effekt der Aufrahmung durch Zentrifugalkraft'' (On the effect of creamingfrom centrifugal force that may be expected on theoretical grounds), and in 1879 it was"Über den Einfluß der durch Erwärmung oder Abkühlung der Milch verursachten
Strömung'' (On the influence of the flow caused by heating or cooling of milk).
The family Prandtl or Präntl, as it was also written earlier, had been resident in Munich
for several generations since the beginning of the 18th century. However, when tracing
back the line, the forefathers are found in the Tegernsee region (a lake in Bavaria). Oneof these forefathers is the carpenter Bartholomäus Präntl, whose eldest daughter Maria is
mentioned in the chronicles in Egern since she founded the Marian Association(Marianische Bund) in her home-town. On 19 January 1770 she died after a godly life,
and the following lines were added to the death register of Egern:"Huius nomen, benigne lector, non leviter praetereas, illius Maria nomen est, quae
plurimas, et verbo et exemplo, animas docuit imitari quoad possibilitatem nostram incastitate Virginem Beatissimam, Fundatrix enim seu auctrix pacti ut vocant Mariani in
Egern, haec erat immo et benefactrix, quod suo labore sudore re sibi lucrata fuerat, Deo,pauperibus et Beatissimae Virgini consecraverat. Conclude bone lector, qua morte
mortua fuerit, quae tam pie vixit. A Daemone quidem obsessa fuit, sed crede non ad
suam, sed ad maiorem daemonis torturam, daemonis inquam utpote tot excellentes
virtutum actus, quos illa quotidie exercuerat, aegre certe ferentis, quia videntis. 19. Jan.
ab hoc inviso hospite et simul a carcere carnis liberata est cum Christo aeternum
regnatura in coelis, quem unice amavit in terris et ante abitum ex hoc mundo saepius in
Domino devotissime suscepit Altaris sacramento.""Her name, dear reader, should not be ignored, as it is the name of that Maria who taught
countless souls by word and example to follow the Blessed Virgin in the virtue ofchastity, as far as this is possible. She was the founder and supporter of the so called
Marianische Bund in Egern and really a real benefactor, who dedicated all that she
earned in the sweat of her face to the poor and to the Blessed Virgin. Draw yourconclusion, dear reader, as to the kind of a death she had after leading such a pious life.
She was obsessed by an evil demon. However, believe (me), that it was no misery to her
but a torture to the demon, to the demon, I say, who was certainly very irritated on having
to see all those outstanding devotional deeds she did day by day. On 19th January, she
was relieved from both the uninvited guest and of the bonds of flesh in order to eternallydwell in heaven with Christ, who was her only love and whom she had often received indeep devotion to God in the holy sacraments before she departed this world.

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Maria's brother Wolfgang Präntl, a carpenter by profession like his father, was the first,
who moved to Munich, where he found a job at the Anger monastery. It would go too far
to list all the family members over generations. So I will skip to the grandfather of
Ludwig Prandtl, Antonin Prandtl, who was born in 1795. As a young man, he was asoldier by profession before he chose a career in the civil service, where he rose to theposition of an actuary (Aktuar) and tax liquidator (Steuerliquidator). At the age of 40 andoccupying a good position, he married Anna Charlotte Hauttmann, the daughter of anelectoral court sculptor. His father-in-law Michael Hauttmann, born in 1772 at
Waldsassen, came from a famous artists' family that is mentioned in Franz Bienback's"History of the Cisterziener Stift Waldsassen". Different members of his family createdwood carvings for the monastery church in Waldsassen. Court sculptor Michael supplied
his artwork for the chambers of King Maximilian I in the old Residenz that weredestroyed by a fire. Moreover, he created decorations in the royal box of the court theatre.
Later on, he devoted himself to making carvings from ivory, alabaster and nacre. Somepieces of this ivory cabinet are displayed in the Bavarian National Museum. Some small
works he created at the beginning of the 19th century passed into our possession. These
works are very fine woodcarvings that are also museum pieces. In 1868, Michael died in
Munich at the age of 96.
Antonin Prandtl and his wife had bought a garden plot in Untergiesing, where they had
set up a small coffee house. Their guests were only young people, most of them artists,
who ventured into the ''strange'' suburb. The generous and liberal atmosphere of life therewith many stimulating ideas from the guests probably brought pleasure into the life ofAntonin's growing children - they were three boys and one girl - and certainly also
stimulated their intellectual development. Their parents enabled them to go to asecondary school and to pass a qualified vocational training. Carl attended Justus Liebig's
chemistry lectures, then went over to study fermentation chemistry and exclusively
devoted himself to the subject of brewery. He was appointed as Assistent for chemistry
and technology at the Weihenstephan Agricultural College. In this specific field, heprovided several scientific works and contributions. He invented the Prandtl filter press
and the Prandtl yeast press, and became the general representative for these brewery
machines. Mention has already been made of the intellectual achievements of theyounger Antonin. After not being granted the possibility to put his ideas in dairy
technology into practice, he addressed himself to the field of brewery. He worked as amaster brewer in Switzerland, spent many years in Hamburg, and returned to Munich in
1884, where he and his brother Carl bought the Giesing Brewery. A decade later, whenelectrification entered the breweries, they could not keep pace with this change in theirsmall plant and went insolvent. However, thanks to their scientific knowledge they could
still act as experts in this field. The youngest child, Anna, married a district judge(Amtsrichter). Alexander, the father of Ludwig Prandtl, has already been mentioned
above.
The living conditions at the Ostermanns' in Freising, where Alexander had rented anaccommodation, were much more modest and less spacious than those of the Prandtlfamily in Untergiesing. Of course, life in the suburb of Munich, actually connected with
the Residenzstadt (Munich) through a horse-drawn tram, was freer and more exciting

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than in the small town on the left banks of the Isar river at the mouth of the tributary
stream Mosach. At the time, when Alexander settled in Mosach City, as the town is often
called, the number of inhabitants amounted to 7000. The spires of four ancient churches
towered up among the old houses. On a hill within eyesight known as the Domberg, there
was a basilica with adjoining monastery buildings in which a seminary was housed. The
widow Maria Ostermann, nee Döbl, was the daughter of a master baker from Freising.
The trade merchant Ludwig Ostermann - as he is designated in the records of the Freisingchurch register -was 22 years older than his wife. He died when the children were still
very young so that Maria Ostermann alone had to bear the burden and the responsibility
for the growing children. Her four children, Magdalena, Ludwig, Leopold and Maria
were brought up from their very roots in strict obedience to Catholic conventions,whatever the reason for this might have been, whether the close proximity of their living
site to the holy centre, or the attachment to tradition. She saw to it that they attended themonastery school and went to church regularly since she had complete confidence in theauthority of the church that was supposed to help her in her difficult task. When
Alexander met his wife-to-be, she was just 14 years old and had not yet finished school.
Right from the beginning, he had a special affection for this little, gentle girl, whoconscientiously took on her domestic and school duties in a touching manner. Many
exercise-books of Magdalena are still preserved. They are full of pious words andmaxims, written in her flowing and flawless handwriting. My father, Ludwig Prandtl,
also kept a few prize books of hers containing lines of appreciation, such as: "1st prize
from the general yearly passing batch for Magdalena Ostermann, student at the FreisingHigh School for Girls. All these gift books were first prizes. Alexander became more andmore attached to this serious-minded and shy girl. He and Leni celebrated their
engagement on 18 September 1872.
He married the 18 years old girl on 19 March 1874 at the parish church in Freising. Bothwere Catholic, but Alexander was not firmly rooted in the church any more. In 1909,
Ludwig Prandtl wrote in a letter to his wife-to-be: "Until a short while ago, I was a strict
Catholic - probably the heritage from my pious mother." He asked Gertrud Föppl about
her attitude to religion and went on to write: "If two have to harmonise with each other,
their religious belief is a very important point. Unfortunately, I noticed with my parents,
who were good souls, but harmonised with each other very poorly, whether in matters of
religion or in the education of children or something else. Apart from the gloom that wascaused later by the sad ill-health, I consider the married life of my parents as a typicalexample for a couple that married for mutual love, but did not get happy due to a lack ofunderstanding for each other".
When Ludwig Prandtl was born in 1875 his mother was only 19 years of age, his father
35. Here are some excerpts from his diary: "The ceremony of baptism was held on 11
February. On 4 May we all went to the shooting grounds to plant 12 fir trees in order tokeep Ludwig's birth in memory. On 16 December, Ludwig fell from the cradle with novisible signs of being hurt. The child was weighed and its growth measured on every
birthday. Entry on 4 February 1879: "Ludwig can count objects up to 10 and precisely
repeat pitches sung to him."

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In the meantime, the young family had moved into an apartment of its own which was
also on the Hauptstrasse at number 41. The entry on 30 April '79: "Ludwig can be sent as
a messenger to (his) grandmother." During these errands, he made many observations on
his own. Full of curiosity, he peeped into the openings of the drains dug up by the roadworkers and was coming home late. He told me what follows from his very earlymemory: As it often used to, the lonely and dreamy child was engaged in playing on thestreet in front of the house when suddenly a downpour came down from the dark clouds.
Instead of hurrying into the house, the child stayed out in the rain since it was full of
excitement to watch the gutter collecting more and more water, draining off the leaves
and paper clippings. At that time, a woman hurried past him with her dress tied aroundlike an apron and with the seam of her wide skirt thrown over her head like a hood. Little
Ludwig then made the unexpected discovery that there were legs hidden behind the skirtsof women that looked the same as those of men. The fashion of those days with skirts
reaching down to the feet and the prudery at that time had kept this a secret from him.
Another anecdote that happened later took place at the railway station. His father took
him there to pick up relatives from the train. After having welcomed the visitors, they all
slowly went along in the crowd trying to reach the gates. However, suddenly the father
notices that Ludwig is not by his side and not seen anywhere. A little excited, the father
runs along the platform. There he sees his little son lying on his belly at the edge of theplatform, directly in front of the locomotive, inspecting and watching the same from thebottom. As he fetches him, the parent is not spare with harsh words. When relating thisstory my father assured me that he was not aware of any wrongdoing; understandably he
was bored listening to the conversation and so he went pursuing his own interests.
Another anecdote related to Easter comes into memory: The painted Easter eggs had been
hidden in the garden for the little boy Ludwig to find. With thoroughness he went about
searching for them and deposited his collected bounties in a basket that his mother kept
ready for him. But what a disappointment there was on his face when he took charge ofthe basket. He had seen at a glance that not all of the eggs he had found actually were in
the basket. He started to thoroughly examine and count the eggs, and to his parents'
surprise, he had stored in his memory the number of Easter eggs of each kind he hadgathered, which did by no means tallied anywhere near the number in the basket. The
reason was that his father, in order to extend the joy, had repeatedly taken the eggs
already found from the basket and had hidden them again, apparently believing that asmall boy could be cheated this way. He then had to confide to his son the whole truth ofwhat he had done, lest he should be blamed for deceit and fondness for sweets.
1880: "Ludwig begins reading printed matter". 1881: "Although Ludwig is lean he looks
healthy. He wants to be a gymnastics teacher." He entered school in the fall of 1881.
1882:" Ludwig ranks first among 82 children!" He also remained at the top in thefollowing years at primary school. In September 1885 he was admitted to the Latin
School that is situated on the Domberg Hill near Freising. On 4 April 1886, Ludwig went
to his Holy Communion, and the confirmation was celebrated on 15 May.
The domestic conditions were quite strained during these years due to frequent illness of
his mother. Her delicate health had been shaken by severe strokes of fate, and she was

14

shattered both physically and mentally. In April 1877 she had given birth to her second
son, who unexpectedly died one week later. A third child, a little girl, was born inJanuary 1879, but suffered from jaundice, of which she died two weeks later. In summer,
Magdalena Prandtl went alone to Altötting to derive comfort from her prayers. In 1881,
she delivered a stillborn child in its sixth month, and the same misfortune recurred in
1883. She has further two miscarriages after which she is completely exhausted. In thelanguage of present medical knowledge it was obviously a case of "Rhesus negative".
Preventive measures could not be taken at that time, since there was only insufficientknowledge in this field.
Magdalena Prandtl often suffered from angina pectoris. In 1888 the depression turned
into a nervous disorder, and she could no longer stay at home. The doctor suggested to
the father to admit her to a psychiatric institution in Munich. When she returned homehalf a year later she was still confined to bed. Since her state of health showed no
improvement she was brought to a nursing home in Neufriedheim.
His mother's sufferings cast a mournful shadow on Ludwig's boyhood years, although hisfather took care of him even more. Magdalena's sister Marie, who was not married, kept
the household for her brother-in-law during those difficult times and looked after her
nephew with much care. She played on the piano with Ludwig and sang with him folksongs and lieder. However, Ludwig's experiences made in his childhood centered around
Alexander's personality, whereas his mother's influence waned more and more due to her
ill health. The father encouraged his son's early interest in physical sciences; he gave him
his books and explained to him the function of the machines and instruments described
therein. He also encouraged him to observe nature, which happened very often during thehiking tours (Wanderungen) they made together in their mountainous home region. His
father's very broad knowledge of nature satisfied the boy's intellectual demands, whichfound expression in many questions. To substantiate his private lessons in nature study,
his father one day brought home a box with two white mice that was kept on the balcony.
Soon, the first baby mice were born and needed care and attention. This became a lively
occupation for the lonely boy. However, within a few months the mice family had grown
to assume fearsome proportions so that the decision had to be taken to stop the successful
mice breeding.
Moreover Alexander was concerned with educational problems. He was vexed thatLudwig often was dreamy and negligent in doing his homework. This taxed his patienceto the utmost so that sometimes he took to very stern measures to cure him of theseweaknesses. In this way, he formed the boy, whose development was so close to hisheart. He meticulously noted down details of Ludwig's development in his diary,
including certificates, illnesses and travels. Alexander's brother and sister, Carl and Anna,
and of course also Carl's children, who were of the same age as Ludwig, often came for avisit. They also met quite often at Munich, the old hometown. My father had very
pleasant memories of the days and weeks he spent in Dingolfing visiting his aunt Anna,
his father's sister. Anna, who had remained childless in her marriage, used to invite
several of her nephews and nieces to stay with her during their holidays, and at no time
did she find their light and cheerful ways in the garden and within the house unbearable.

15

Ludwig was at ease and felt very much at home with this aunt, who was the wife of
Oberamtsrichter Kastner. Among his cousins, he forgot his unhappiness over his own
circumstances. His relatives of the same age were his best playfellows and could
substitute the lack of any siblings at least in part. Ludwig was attached to them for hiswhole life. One of them wrote her cousin Ludwig in 1944: "I was thinking of how you
used to ponder over equilibrium and statics. Do you remember your after-dinnerexperiments with bottles, plates, forks and knives that mostly reached fearful heights?''
At that time, also the grandmother Anna Charlotte Prandtl was living at her daughter's inDingolfing and was very happy to see her growing grandson visiting her often.
The travels he did with the father during the school holidays were also a kind ofexperience he later recalled with pleasure. These vacations, "Vakanzreisen" as Alexander
noted in his diary, took him either to the lake area around Munich or, via Innsbruck, tothe valleys of the Austrian mountains, or sometimes even to South Tirol, to Bozen and
Meran. When they stayed in one place a little longer during the holidays, Ludwig spent
his time making drawings of the landscape paying attention to details. His hometown
Freising often was also an object of his eagerness to draw. The enthusiasm, with which
he worked on the details, is an evidence for his talent at that age and his patience at work.
Alexander attached importance to the development of musical talents of his son. At theage of nine Ludwig got his first piano lessons by Professor Durmayer. The father himself
liked to play the piano and used to give music performances for evening entertainment
with a teacher in Freising. He had also achieved certain virtuosity in the art of playing thehorn, just like his brother Carl. Once Alexander and Carl gave a public performance withhorn duets in which the programme lasted almost two hours. The occupation with music
probably fulfilled Alexander's inward needs, as his religion did not provide him with thenecessary refreshment. His attitude towards the church was more and more determinedby denial. He could not reconcile the dogmas of the Catholic belief with his scientific andcritical thinking. In particular, the dogma of the Pope's infallibility that was proclaimed in
1870 later appeared to him as being unacceptable. Probably, he was under the influenceof the group of Munich professors, who protested together against the dogma(Altkatholiken). In 1886, Alexander left the church for ever.
In Ludwig's life, the father's influence in religious matters cannot be overlooked. The
responsibility the father had to bear for the care and welfare of his child needed
considerable time due to the ill-health of his wife, which however he could not afford,
since his job required frequent travels. In the fall of 1888, he therefore decided to admit
Ludwig to the Ludwigs-Gymnasium (Grammar School) in Munich, an education
institution under royal patronage, and spoke with the Director Willy von Coulon. Ludwig
was put up in the boarding home Hollandeum and went home only during the holidays.
Sometimes my father spoke of these times as difficult ones for him. His experiences inliving together with other schoolboys were not pleasant, since he often was teased anddomineered by stronger and defter schoolmates. Inwardly, he was helpless against these
insolences and suffered silently. At the end of the school year, his father took him back to
Freising, as his mother had slightly recovered from her illness. However, as mentioned,

16

earlier the recovery was only temporary, her health taking a turn for the worse soon. For
the following two years, Ludwig attended the Latin grammar school at Freising.
Thereafter, when his mother had to retreat from all family life, the boy was sent on the
Munich Gymnasium again. This time, he was better able to assert his position and foundfriends. One of these friends, Oskar Winsauer, who had become the City Priest at the
Heilig-Kreuz Church in Munich-Forstenried in 1940, remembers these days at the hostel
and the school:"6. April 1941.
Lieber Studienkollege!
Und jetzt schreibe ich doch! Oft schon wollte ich mich hinsetzen, um meinen lieben
Koäven und Mitzögling vom Hollandeum zu schreiben und zu gratulieren, besonders
damals, als im 'Neuen Münchener Tageblatt' Dein Bild erschien samt der Mitteilung,dass Dir eine hohe staatliche Auszeichnung zuteil geworden ist T- aber immer hielt michder Gedanke zurück, was wird der berühmte Wissenschaftler um einen einfachen Pfarrer
scheren. Nun habe ich Klotz und Reiter getroffen, die mir mitteilten, dass Du ihnen
freundlichst ein Lebenszeichen gegeben habest. So möchte ich Dir auch ein
Lebenszeichen geben und Dir einliegend eine Urkunde aus dem vorigen Jahrhundertübermitteln. Armer Leidenskollege! Aber, was musst Du auch Deine Karte beschmieren?
Übrigens wird das kaum der einzige Pultarrest gewesen sein, den wir erhalten haben. Ich
wenigstens brachte deren 60 pro Jahr zusammen - weil ich mir erlaubte 'mit Tinte ins
Buch zu schreiben' oder 'wegen geräuschvollen Niesens' und dergleichen mehr - meist
aber wegen Unaufmerksamkeit.
Solltest Du einmal wieder während Deiner Ferien nach München kommen, würde ich
Dich herzlich bitten, mich anzurufen.""6 April 1941
Dear Fellow Students!
After all, I am writing you now! I often wanted to sit down to write and congratulate my
Koaeve (chum) and fellow pupil at the Hollandeum, in particular at that time when yourphotograph appeared in the Neues Münchner Tageblatt together with the announcementthat you have been granted a national honour T1---but one thought always held me off:
What would the famous scientist care for a simple priest? Now I met Klotz and Reiter,
who told me that you have been kind enough to give them a "sign of life". I wish to give
you a "sign of life", too, and I am enclosing a document from the last century. Oh, poor
companion in misfortune! But why did you have to smutch your card? By the way, thatwould hardly have been the only punishment (Pultarrest) we got. For me, the total came1

Possibly it is: Freistaat Bayern, Goldener Ehrenring mit dem Bayerischen Staatswappen, München,
7.5.1926 (Free State of Bavaria, Golden Ring of Honour with the Bavarian Coat of Arms, 7 May 1926)

17

up to 60 per year---since I permitted myself to 'write with ink in the book' or to 'sneeze
aloud' and some things more alike---but mostly due to poor attention.
If you happen to come to Munich again during the holidays I would request you from thebottom of my heart to call me on the phone."
In all these years, Ludwig's performance in the scientific subjects was far above average
and after some time, this intellectual superiority did earn him the respect of hisclassmates.
In 1894, he could start studying at a university and he stayed in Munich. For four years
he was a student attending lectures at the Technische Hochschule in Munich.
In the meantime, the home in Freising had been broken up completely. Alexander, who
was suffering from heart weakness, retired at the age of 52 and moved over to his sister
Anna at Dingolfing with the burden of fate resting heavily on him. He died there on 17
March 1896. In 1898, after much suffering, his wife Magdalena was relieved of further
suffering by death. Ludwig stood alone in life now. He was completely absorbed in his
science, which led him to success after a few years only. I am deeply touched to say that
it is very sad, indeed, that his parents did not live to see this joyful development.

18

3. Years of study---MAN-appointment
Ludwig Prandtl's interests focussed on physical and technical subjects, so the decision on
the subject of study at the university posed no difficulties. He chose to study mechanicalengineering. Following the advice of his caring father he began in August 94 itself, - hehad completed school in July---a three-month period of practical training at a workshop.
This apprenticeship, which had to be passed before taking up the study at a university,
took him to the mechanical engineering company MAN at Nürnberg where he had applied
for an employment. There he worked in the foundry as well as in the pattern shop. After
this period of practical training, in autumn 94, he took up his studies of the theoreticalparts at the Königliche Technische Hochschule (Royal Technical College) in Munich.
His teachers in the most important subjects were: Professor of Mechanics, August Föppl;Professor of Mathematics, S. Finsterwalder; Professor of Physics, L. Sohnke; Professorof Theory of Machines, M. Schröter.
He used the time during the holidays he used for further practical work, partly again in
Nürnberg. In 1898 he graduated from the Technische Hochschule as a mechanicalengineer.
It is certain that these years of study in Munich widened his horizon substantially. He
became a member of a student fraternity called Münchner Gesangverein by name, whichbrought together mostly students oriented towards music. My father had a beautiful bass
voice, and he liked singing in a choir for several voices. Just as his father once did, he
too picked up a wind-instrument and learned to blow on the waldhorn (French horn). A
member of the fraternity, who wrote him 40 years later, referred to this in his letter of 5
May 1939. Hermann Peckert wrote the following: "I presume you still remember me;
although perhaps not as clearly as I remember Trompetenprandtl (trumpet Prandtl) withhis full black beard and his cheerful temperament that was always unshakeable. In all
likelihood, this has not changed. Possibly you have given up trumpet blowing after you
did enough studies of the Luftwirbel it generated" However, the piano remained his
favourite instrument. After six years of practice, he had reached a level of respectableproficiency. He played sonatas of Beethoven, Haydn, and Mozart. He sang Schubert's
lieder to his own accompaniment on the pianoforte.
The students (members of the fraternity) also went on hiking tours in the surroundings. In
one or the other small village church, he climbed up the steps to the organ, examined thebellows and played preludes in all registers, one following the other. He felt a special
kind of love for this versatile music instrument.
Much later, when his Institut at Göttingen was expanded, he even toyed with the idea of
having an organ installed in one of the halls.
There were several occasions of social gathering. My father told me of a "laundry
festivity" in the carnival period, which was celebrated with much colourful imagination.
Most of the women, dressed in the costumes of Dutch women, brought laundry baskets

19with them. Clotheslines were put up everywhere in the hall on which everyone could
hang up her own clothing. The decent custom was of course respected---no piece ofclothing that could not be named in public! But towels, serviettes and pillowcases hungvery soon on the clotheslines all in a tumble. And, in these surroundings that resembled adrying loft, dancing went on merrily.
He was a frequent guest at the house of his uncle Carl Prandtl, who then lived in Munich.
He made preparations for hiking through the mountains with his cousin Carl or heaccompanied his cousin Clara on her walks along the Isar or through the Nymphenburg
Park.
When Prandtl passed the final examination in 1898 with the grade ''sehr gut'' ("verygood"), Professor Föppl offered him the job of a Hilfsassistent, which he gladly accepted.
The post, which was meant for one aspiring to earn a doctor's degree, was assigned for
one year only. Now, after completion of his studies, Prandtl should be conscripted formilitary service. For this reason, Professor August Föppl wrote the following letter ofrequest to the Commando of the Royal Pioneer Detachment:"In the beginning of the new academic year in autumn of this year, we plan to starttutorials in the mechanical-engineering laboratory of the Königliche Technische
Hochschule, of which I am the director, and for this purpose, we intend to employ
another assistant. Since this branch of study is being newly founded, it is crucial to fillthis position with a properly trained engineer. Herr Ludwig Prandtl, who will be leaving
the Hochschule at the end of the semester and is due to enter (military) service, isespecially qualified for this post. If it is permissible to postpone Prandtl's conscription for
military service by one year, I would earnestly request the Königliche Commando (TheRoyal Command) to do so. Thereby, this would render an important service to theeducation at the Königliche (Royal) Technische Hochschule. Hoping that my request
would be granted I remain your most devoted,
Dr. A. Föppl, Royal Professor."
The request was allowed. The period when Prandtl worked with August Föppl in his
mechanical engineering laboratory can be dated exactly: from 1 October 1898 to 30
November 1899. Besides attending to the duties of a teaching assistant at the courses, heworked on various experimental and theoretical problems on strength of materials andelasticity. One of them was worked out and submitted as his doctoral dissertation(Doktorarbeit).
It was customary in those days for an Assistent to be invited by his professor to his homealso. This custom was an attempt to instil in the young student a feeling of security inmatters of human relationships. As first and foremost of course, the invited young man
had to drive in by cab on a Sunday, present his visiting card to the house-maid and,removing the white gloves from his hand, to be greeted by the professor and his wife in
the drawing room. The Föppl family did not stick very closely to this etiquette, so Prandtl
could feel at ease with them. When he was invited to this family for the first time, he also20

got to know the children. At that time, my mother, the family's eldest daughter, was 16
years old then, a shy blonde. They also had two sons, both going to the Gymnasium, anda little sister at the age of six. When my grandmother learned that the new Assistent had
recently lost both of his parents, she often invited him for lunch or dinner with theirfamily.
One of the two sons, Professor Ludwig Föppl, Prandtl's future brother-inlaw, has given
me a small note he made for himself under the heading "Memories of Ludwig Prandtl".
His description of the personality and efficacy of his brother-in-law would add to myaccount in many respects. It begins with memories of those days:"The first meeting with Ludwig Prandtl that the author of this note still remembers could
have been in the year 1898 when the twenty-three year old Prandtl was an Assistent of myfather August Föppl, and was invited now and then by my parents for Sunday lunch. He
was glad to stay on with us for coffee after lunch, especially since my mother treated him
with motherly affection. This practical woman with a kind heart felt that this young man,
who was so lonely and was exposed to life without any womanly help, shouldoccasionally be taken under her wings. She gave him advice in some practical matters,
which certainly helped him to master his daily life. Once, when she saw that the hangerof his overcoat was torn off, she sewed it on, and when Prandtl took leave of us, he was
not just a little surprised that brownies had been at work in the meantime and put his
overcoat back in order. During one of such visits by Prandtl, in the Christmas season---I
was eleven years old, my father suggested to me after lunch to play a Christmas carol on
my violin for the visitor. I was hesitant and my playing was only a modest success. I do
not have that fine ear that Prandtl had, and I can imagine today that it was far from apleasure for him to have to listen to me. After I finished playing, he remarked that theviolin seemed to be a little out of tune. I noticed with what care he expressed his criticism
in order not to hurt me.
When he was my father's Assistent, Prandtl worked on his doctoral thesis. The subject of
his thesis that he chose all by himself was "Kipperscheinungen an belasteten Staeben"(''lateral deflection of loaded bars'').
Since this first work of his, which he carried out entirely on his own, already shows thecharacteristic signature of the later Prandtl, it is appropriate to go briefly into the problem
and the way it was handled by Prandtl. Consider a T square kept horizontally, clamped at
the T end, and the other end (the vertical longer edge of its cross sectiom) loaded by anincremental weight. In this configuration, a proprtionately small weight causes a lateraldeflection of the loaded end. Prandtl introduced the term Auskippen (''deflecting away'')
for this movement, which has been generally adopted since then for such phenomena inloaded structures and has a great practical significance in building design/construction.
Although an explanation for this ''deflecting away'' had been sought several times before,
it was left to the young Prandtl to succeed in completely explaining the observed
phenomenon. Following his line of thoughts that led him to the solution of the problem inthe dissertation, the close proximity of the mathematical approach to the observed

21

geometry, as the loaded structure tilts away laterally, is striking as particularly
characteristic. His extraordinary skill at capturing the essential elements of an observed
phenomenon through a suitable mathematical-physical ansatz is already manifested byhis first scientific work.
With this dissertation completed in 1899, Prandtl could not get a doctor's degree at theTechnische Hochschule München (this institution was given the right to award doctor's
degrees only in 1900) , so that he submitted the work to the university. The
Philosophische Fakultät of the Munich University appointed the renowned
mathematician Ferdinand Lindemann as the referee. The examiner in the main subject
was Professor Leo Graetz. The viva voce took place on 29 January 1900. Since thefinding in the dissertation was that the key differential equation for lateral torsional
buckling belongs to the type of Bessel's differential equation and since the numericalevaluation of the Bessel's function of a certain order was done for the first time in thisdissertation, the mathematician was interested in the work, and Prandtl passed thedoctoral examination with a good grade." (Quote from Ludwig Föppl)The title of the dissertation was: Kipperschenungen, ein Fall vom instabilem elastischem
Gleichgewicht (Lateral torsional buckling: A case of unstable elastic equilibrium). Its
publication was a slightly long drawn affair; the dissertation appeared in Nürnberg in
1901[28].
Of course, the printed dissertation was immediately sent to August Föppl. He replied withhis letter dated 21 February 1901:"Dear Herr Prandtl:
I have been very happy with the fine piece of work that you sent me, and I went throughit immediately from beginning to end. I was especially very pleasantly surprised at thedetailed and circumspect discussion of all the different cases connected with lateral
torsional buckling (Kipperscheinungen). I had not known before that your work would
cover such a large orbit of phenomena. It is for the first time that I have come across suchan excellently accomplished piece of work from one of my students, which, therefore,
makes me all the more happy."
By now the period of study in Munich was completed, and the professional career began.
He wrote to the government building officer, Baurat Anton Rieppel (known as thebuilder of the Müngsten bridge, the highest railway bridge in Germany) in Nürnberg in
reply to a letter from him: "In the matter regarding your valued offer I would be very glad
to take over the set-up of the laboratory, and I am ready to enter into an employment withyou on 1 January. Once everything is running smoothly in the laboratory, it will perhaps
be possible for me to change over to the office of either gas or steam engines. But thesethings are only in the future, which need not be discussed here now.
I have also taken the liberty of enclosing a copy of the testimonial given to me by Herr
Professor Föppl, at the time of termination of my work with him.

22

I am looking forward to your favourable decision and, if need be, am willing to comeover and talk with you in Nürnberg at any time you desire."
On 1 January 1900 he joined Maschinenbaugesellschaft in Nürnberg as an engineer. At
that time, the company merged with Maschinenfabrik Augsburg to become MAN. Here,in the plant that was already familiar to him, his work was that of a Mitarbeiter in thedesign office. There were plans for a new works building, and drawings had to be madeready for installation of the machinery. Among other things, the young engineer had, theassignment to make improvements to a defective plant for pneumatic suction of theshavings in the new wagon division. This was urgently called for, since work in the
carpentry was hampered by shavings that were accumulating in bulk. It also turned outthat the dust and the fine wooden shavings, falling off from the woodworking machines,
were causing much suffering to the workmen in the carpentry. Because of the resulting
air pollution, some of them came down with lung ailments. The suction line was
supposed to extend over several barracks. This was how Prandtl's attention was drawn for
the first time to the problems in fluid flow. On going through the literature on thisproblem that was available to him, he could only verify that there was little known forcertain in this area. He therefore set out to obtain clarity on several open issues throughexperiments conducted with relatively rough methods to start with. Based on the resultsof these studies, the shavings suction plant was entirely rebuilt. The problem was solved
successfully by the design of a unit incorporating a cyclone separator, and very soon it
was realised that it was possible to reduce the power to be installed to a third of its former
value by the choice of better shapes and proper sizes of the piping, and to achieve
uninterrupted operation. From that time on, the factory took up production of Prandtl's
shavings suction plant in its manufacturing program, and soon received many orders.
During the vacations he regularly went to his relatives in Dingolfing or to Munich, andnever missed to meet there his respected university teacher August Föppl, who wasinterested in following up Prandtl's career.
In the year 1901, a successor was to be appointed to the professor's chair for mechanics in
Hannover that had become vacant. August Föppl, who was consulted in this matter,suggested among others the young engineer from Nürnberg, whose doctoral dissertation
had proved him to have great talent. Early in August, Prandtl was informed by a letterfrom the Prussian Ministry for Education that he, among others, had been proposed forthe appointment as professor to the chair of mechanics in Hannover, and that he shouldcome to Berlin for a discussion if he intended to accept this teaching position in the eventof his selection. A few weeks later, he was informed that he had been chosen. Prof. Carl
Runge, who had been holding the chair for mathematics at the Technische HochschuleHannover since 1886, must have exercised a decisive influence on getting the vacant post
offered to the young engineer. On 21 August, the appointment order was signed:"Wir Wilhelm, von Gottes Gnaden, König von Preußen thun kund und fügen hiermit zu
wissen, daß Wir Allergnädigst geruht haben, den bisherigen Ingenieur Dr. Ludwig

23

Prandtl in Nürnberg zum etatmäßigen Professor an der Technischen Hochschule inHannover zu ernennen."''We, Wilhelm, King of Prussia, by God's grace, are pleased to announce and hereby
make known that We appoint, the engineer Dr. Ludwig Prandtl, till now in Nürnberg, tothe professor's chair at the Technische Hochschule in Hannover.''
On 30 September, after giving up his engineer's position in Nürnberg, he travelled to
Hannover as a Prussian civil servant. Being 26 years old, he was the youngest professor
in Prussia. He gave lectures in mechanics in the Division of Mechanical Engineering andheld tutorials in graphic statics. The examinations that he had to hold in a semester werelarge in number, and were an additional duty. However, he did find enough time topursue his own research on fluid flow phenomena. The Nürnberg experiences on the lawsof fluid motion had left many of its details unanswered. For example, the question was
still open as to why the air stream in a conically expanding pipe does not follow the wallsof the pipe, but almost flows as a free jet in the middle of the pipe.
He wrote of his impressions of his move to his relatives at his Bavarian home. The
frequent letters, which were conceived as circulars, went to his father's brother and sister,
both of whom were now living in Munich, and to the family Ostermann in Freising.
Letter of 26 October 1901: "For the time being I have left my furniture with my Nürnberg
landlord and landlady. Since I happen to be in Nürnberg just now, I also wish to tell how
my farewell went off there. Of course, I was at several farewell parties, once at the
Nürnberg Philister Union, where I had the opportunity to throw a beer party. Then an
exchange of views with the men's choral society. A farewell song with horn solo (he blew
the horn part himself) 'Behüt dich Gott' (may God protect you). The next day at seven in
the morning, I steamed off into fog. At the Hochschule in Hannover almost all Gaus of
Germany are represented, we have Bavarians, Swabians, Badenians, Kurhesses,
Austrians, and, of course, a pride of Prussians. (I have not yet taken my oath of office, so
for the time being I am permitted to feel as a non-Prussian.)A little more about my search for living accommodation: I received 60 offers in response
to my advertisement, but I did not find the right one among them. A colleague got me thesame, and I am quite happy." (He moved to Nienburgerstrasse 12.) "The location issomewhat like Königinstrasse in Munich, with the only difference that here, I am better
entertained by an electrical streetcar/tram rattling along, that I see, hear and feel. Apartfrom this, the location is very beautiful. Just opposite to it, there is a park, behind it you
sometimes see a sunset, which is, however, mostly not to be seen due to fog.
Letter of 3 January 1902:"By the way, I wanted to tell you about my life and doings in
Hannover. First the language: it is said that the purest and best German is spoken in
Hannover, i.e. by the people. Now, listen! My first discovery was that I could understandthe waiter at the hotel only with difficulty, and the same happened with the shopkeepers.
But then, I soon made the big discovery that the local language could have been derived
from German when certain rules of pronunciation are observed. (After all, the dialect of24

the old language cannot be described that easily, couldn't it?) The pointed "Stein" ismeant literally, the 'ei' being pronounced like 'A' in Kas at your place. Once these rules ofpronunciation are learned, you will find that the people here speak written German quite
well.
Even otherwise, Hannover has various peculiarities: a streetcar driven by accumulators(there are no overhead lines in the heart of the city). The streetcar network is the largest
in Germany after Berlin. Streetcars go to every nook and corner out into the Lüneburg
Heide, as if those in Munich would go to Freising, Dachau, Starnberg, Wolfratshausen,
Sauerlach and Grafing.
I was assured that Hannover lies on seven hills. But I have not yet found all of them. One,I discovered without any help. That is the Schneiderberg which I cross every day to go to
the Hochschule. It is so high that the even the tallest man cannot look over it (that is theway it is expressed here). The weather here changes between being foggy, wet or windy,
for a change wet and foggy or wet and windy. This climate could be the reason, why
windows open here outwards so that there is no place for a winter window in the front.
Something I miss here is our good home bread less salt and no spices. Over here, thebread is eaten only with butter (even beggars do not accept it in another way)."
Letter of 1 July 1902:"One day at the beginning of May, I took part in a geological excursion to the Harz where
we saw, in rain, the beauty of the mountains and the stone formations, and despite the badweather---these were very beautiful, indeed; the Harz is an excellent mountain, theBavarian Woods cannot be compared with it, at least not as I remember them. The parksof Herrenhausen are now splendid, everywhere the lilacs are blossoming, the nightingales
are singing and the frogs are croaking. Even at the Hochschule, May has not passed bywithout leaving its trace: A colleague, until then my daily companion at the table, isengaged. I think I am the only one among the younger Dozents, who is not engaged. In
spite of this, the girls of Hannover have no chance of capturing me in their basket for thetime being. I still think the one for me should be able to cook Knödel and Nockerl and notderive a sense of pleasure in adding raisins to spinach."
His attachment to his Bavarian home made it difficult for him in several respects todevelop an intimate relationship with the Hannover life style.
Even in matters of socialising at the Hochschule, there were differences in interpretations.
Formality was emphasised in all matters. Once, my father was asked to participate in asmall stage performance. A Bavarian group of singers was supposed to come on the stage
and the men were to appear dressed in leather shorts. When the young Dozents came to
the rehearsal in the traditional Bavarian costume, flesh-coloured tricots were distributed
to them to be worn underneath the leather shorts, since it was considered beyond thelimits of permissible decency for the society ladies to be shown men's bare knees.

25

On the other hand, a very deep and friendly relationship developed between Professor
Carl Runge, a man from Bremen by birth, and Ludwig Prandtl, 19 years younger in age.
My father revered his witty and versed colleague, and spent many happy hours in his
house in Kirchrode. In her reflections on Carl Runge's life, his daughter Iris [44]writes:"Those days, Runge often brought with him a young friend Ludwig Prandtl withwhom he liked to talk over scientific matters. Carl Runge had also exerted his influence
to get Prandtl called for the appointment to this post. Very soon it became evident that
this new friend had a good understanding of music and a beautiful bass voice." (TheRunge family attempted to perform Bach's St. Matthew Passion (Matthäuspassion)).
With his sonorous voice in bass, the father Runge in tenor and the daughters in sopranoand alto, the full timbre of all voices could be achieved, although the untrained voicesneeded many trials to achieve a tolerable result."
Letter of 30 January 1904 to the relatives:"On Christmas Day, I spent the evening with my colleague and fellow Philister Runge (4girls and 2 boys, therefore a house full of life). I go there quite often now, we have many
common scientific interests, music is created diligently (mixed quartette)."There were several other colleagues who soon became his friends. One of these was Dr.
van Hanstein, a Privatdozent for literature, who often invited him to his home. In 1903,
Prandtl happened to move into an apartment situated diagonally opposite to his friend's
home so that they lived in immediate vicinity.
3 January 1903 - he had moved to Militärstrasse:"The last quarter was full of work for me, so much, that I do not wish for it again. What
forced me most to work was that I had begun to hand out autographed notes to all my
lectures in which the most important points were put together. I was forced to work out
my lecture material with such a care that I could use it over several years. I have madesignificant progress at my research work."
He had built for himself a small experimental facility with a water tunnel. The water thatwas set flowing with a paddle-like mechanism was first mixed with glittering leaf-likeparticles (iron glitter) in order to visualise the motion in the flow resulting from different
experimental configurations. Once he told his student Dr. W. Tillmann how he got theseiron glitter by chance: One day, when Prandtl was working with MAN in Nürnberg,,
construction workers came to him. They brought with them reddish coloured chunks
from an excavation pit and thought they had stroked soil containing copper. On slurrying
the material in water, he discovered tiny imbricated particles with which a flow could bemade visible. Under the influence of a shear, these suspended particles assume apreferred orientation. Light reflected by the particles then convey an image of the flow.
Chemically, these glittering iron filing particles were made of iron oxide. By slurrying of
the discovered material in a large number of self-made cardboard saucers, he had
obtained a large quantity of iron glitter suitable for flow visualisation. A similarly well

26

suited raw material has not been discovered again. The stock of iron glitter travelled with
him to Hannover and Göttingen when he was called to accept chairs in these places. Withthrifty use, the collected stock was sufficient to last for fifty years before it was finallyreplaced by a synthetic pearlescent pigment.
Prandtl worked late into the night, drawing and doing calculations in search of laws. His
experience then taught him the lesson that eagerness at work taken too far can lead toexcessive strain, and thereafter he consciously exercised moderateness in pace of work
despite urgent problems.
Letter of 23 January 1903:"Suddenly, I have had too much work in February, and it is still affecting me, i.e. I get
tired from work very soon. As a diversion I have started to take photos."
However, even thereafter, his daily work routine ran into many more hours than usual,and it is to be supposed that in those days he worked throughout the night. He led asomewhat retreated life, and over the Whitsun/Pentecost holidays, he went on a longer
hiking tour through the Wesergebirge (the hilly country on the Weser River) whichbrought him enough rest. He included small sketches in his travelogues to illustrate hishiking route and his impressions of the landscape.
Letter of 23 June 1903:"By train to Coppenbrügge, hiking through the Ith hills, luncheon in Lauenstein, keep
moving along the crest, rest on the Hammerslust rock, in the evening to Escherhausen.
Next morning via Homburg (old castle in ruins on the high mountain) to Stadtoldendorf,
from there on the Ebersnacken and the Königszinnen. Going aboard at Bodenwerder andon the Weser up to Hameln. Sightseeing of the town, swimming in the Weser. Next day
in Ohrberg (nice park), swimming in the Weser, back home in the evening. The tallest
mountain that I saw was 495 m high!"
Letter of 30 January 1904:"I start with my bidding farewell to the beautiful land of Bavaria last September. As you
may know, I went to the meeting of scientists and doctors (Naturforscher- undÄrzteversammlung) to Kassel, at that time. I do not repent having participated in thismeeting. I came to establish many valuable contacts there, particularly withmathematicians and physicists. My own lectures were somewhat afflicted with the factthat both were scheduled for the afternoon of the last day. One was received withapproval, the other (on vectors) met, as expected, with differences of opinion. At the endof the conference, a number of mathematicians and physicists followed an invitation to
Göttingen that offers extraordinarily interesting things and personalities. The hospitality
there is great. I was put up at the astronomer Schwarzschild's, had my afternoon lunch atProfessor Nernst's the chemist, and Mr. Ramsay the English chemist, was seated twoseats next to mine. Soon after my return to Hannover, a business of a different kind27

started in full swing: holding examinations in the forenoon, holding examinations again
in the afternoon, and so on for 4 weeks. Lectures have started in the meantime, then there
were again examinations besides the lectures, and so did the time pass until Christmas.
Since 5 January, the lectures are going on again. Moreover, there was lot of other work:
extended publications of my lectures, a few other publications are in preparation, andthen the committees, so there is no lack of work for me. In spite of this, recently, on theEmperor's birthday, I allowed myself the pleasure of doing nothing the whole day long. I
went skating and on a walk."
Then he got back to his diversified work.
In spring, an inquiry came in from Geheimrat Felix Klein from Göttingen whether
Prandtl would be willing to take over the Institute for Technical Physics that had beenheaded by Professor H. Lorenz. This institute that involves the position of an
ausserordentlicher Professor was founded upon the initiative of Felix Klein, the creative
mathematician and organiser of mathematical-physical-technical education, when funds
were made available for this purpose by the Göttinger Vereinigung zur Förderung derangewandten Physik und Mathematik ("Göttingen Society for the Promotion of Applied
Physics and Mathematics") under the chairmanship of Henry Th. Böttinger and F. Klein.
In a letter to Klein, Prandtl's earlier boss at MAN, Baurat Rieppel, expressed his opinion
on this proposal for filling this post: "7 March: I hold the opinion that your idea toprimarily consider Herr Dr. Prandtl for this post is very fortunate. Herr Prandtl is an
extraordinarily talented person and, at the same time, very diligent. His amiable characteris a guarantee for a pleasant working atmosphere..."Runge from Hannover expressed himself as follows: "I hold a very high opinion of his
talent and will do everything within my powers to keep him at our university. . . "On 22 April, Karl Schwarzschild wrote to Klein in the same matter: "I got a letter from
Runge on Prandtl---Dismal prospects!"
On 4 May, Prandtl sent a provisional reply to this offer to Klein.
"Letter of 4 May, Hannover
To Prof. Felix Klein
Respected Colleague:
As promised, I would like to inform you about my considerations regarding theprofessor's post in mechanical engineering in Göttingen. On the one hand, I am attracted
by having my own laboratory and more of leisure time, and last but not least the nicescientific interaction in Göttingen. On the other hand, my work in Hannover during theperiod of almost three years of my stay here has become very dear to me. I would
probably be exchanging my large sphere of activity here with a much smaller one. I
would not attach much value to my not having a seat (with voting rights) at the Fakultät
in Göttingen, being an a.o. Professor, whereas I am a regular member (with full rights) in28

the department here. My most serious misgivings come from my feeling of belonging toengineering. For a long time, I have been toying with the idea of putting my efforts inenhancing the scientific content of teaching at technical universities (Technische
Hochschule). From this standpoint, my change over a university only appears justifiable,
as this position---which, I think, will not be my final one---will give me the extraordinary
opportunity of elevating my scientific level and prepare myself for tasks in the future.
Furthermore, the exchange of thoughts with theoreticians will help to solve many of the
problems which are close to practical application."
The salary of 6500 Marks per annum that he asked for was the same as his pay at theTechnische Hochschule Hannover.
The decision on the matter was supposed to be taken by the ministry in Berlin. Klein had
forwarded the recommendations with a personal letter and had made the following points
regarding Prandtl: "Prandtl's works stand out for his sound knowledge and mastery ofmathematical tools in combination with the power of intuition and great originality ofthoughts. In addition, Prandtl has a particularly deep interest in pedagogics."
Since the ministry did not approve of the pay demand, Henry von Böttinger (thecommercial head of the company Farbenfabriken, and formerly, the Bayer company inElberfeld) wanted to provide the sum falling short of the 6500 Marks from private funds,.
So, as far as the matter of pay was concerned, the offer for the appointment to Göttingen
was to be given serious consideration. Prandtl travelled to Berlin for negotiations andasked for some time to think it over.
In a letter of 25 June to Professor Klein, everything was still in suspense.
"Hannover, 25 June 1904
Respected Herr Geheimrat!
The decision has not yet been taken, I do not yet have the call in writing. The reason forthe delay is that the Hannover colleagues have put in vast efforts with the ministry toretain me here. I also wish to take this opportunity to inform you that I had to struggle
with myself to cut all the links that hold me here, and much effort has really been put inkeeping me here. The Civil Engineering Department is setting up a new and beautiful
Solid Mechanics Laboratory (Festigkeitslaboratorium), which is to be completed shortly,
and a few members of this department have offered to leave the same to me for mydiscretionary use, and so on! After weighing the pros and cons of one against the otherfor long, I finally tend to Göttingen."On 1 July, the decision was taken in favour of Göttingen.
However, the negotiations with the ministry were not yet concluded. Finally, on 1 July,
they had reached their goal, and Prandtl was in a position to give his final assent. On a
postcard to Klein, he wrote: "Respected Herr Geheimrat! After having just received a29

letter from Herr (Ministerialrat) Naumann I have decided to accept the Göttingen offer of
appointment."
Although it is unusual to choose to take a retrograde step in the academic career, i.e.
giving up the position of an ordentlicher Professor to take up one of an
ausserordentlicher Professor, Prandtl considered this an opportunity to devote himself to
his scientific research. His Doktorvater, August Föppl, had strongly advised him not to
accept such an offer. It goes against all reason to degrade oneself professionally. But
Prandtl's creative spirit placed the accents differently. He was attracted to the prospect of
having much more freedom in the new place for pursuing his problems and researchideas. He was also convinced that he would later have an opportunity to regain theposition of an ordentlicher Professor again.
Prandtl cherished a great admiration for the mathematician Klein, by whom he also felt
personally attracted, and whose protectorate held the promise of a good working
atmosphere.
Klein had special goals for teaching in the branches of mathematics and science. To thestudents, whose aspirations were often to take up a profession of a more practical nature,e.g.. working in a factory or teaching at a school, he wanted to impart an education thatshould be related more closely to this purpose. In those days, German universities had
little connection to engineering or industry. The American universities served as an
example. He was a superb organiser, and his activities were widely recognized. Thanks to
his initiative, a number of chairs and institutes were set up in Göttingen that were
designed to serve practical applications in the field of science. In Prandtl, he had found ateacher who, as an engineer, could develop his subject matters entirely from the practicalpoint of view. Felix Klein became his trusted friend, who participated in all his plans andalways supported him through professional discussions in his scientific field.
On 12 August 1904, just before moving to Göttingen, he travelled to a conference in
Heidelberg. It was the III International Mathematicians' Congress (der III. Internationale
Mathemathiker-Kongress), where he lectured on his new scientific theory called theboundary-layer theory [35] (Grenzschichttheorie). It was the result of his experimental
and theoretical studies mentioned earlier. This talk caused a sensation among theparticipating mathematicians, who followed his new ideas on flow phenomena with greatinterest. A fundamental step in knowledge had been taken that would be significant forthe development of aeronautics. Now, he had become famous in scientific circles.
In his memoirs, Professor Ludwig Föppl comments on Prandtl's boundary-layer theory:"In view of the importance of this work, I would like to point out to its essentials. By thattime, there had been no theoretical explanation for the drag experienced by a body in a
flowing liquid or in the air. The same applies to the lift on an airplane. Classicalmechanics was either based on frictionless flow, or, when friction was taken into account,mathematical difficulties were so enormous that hitherto, no practicable solution had
been found. Prandtl's idea that led out of this bottleneck was the assumption that a30

frictionless flow was everywhere with the exception of the region along solid boundaries.
Prandtl showed that friction, however small, had to be taken into account in a thin layer
along solid walls. Since that time, this layer has been known as Prandtl's boundary layer.
With these simplifying assumptions, the mathematical difficulties just mentioned, thatshow up in classical fluid mechanics of a flow with friction, could be overcome in a
number of practical cases. Prandtl could prove theoretically and experimentally that theboundary layer can separate from the surface of a body immersed in a flowing fluid at
suitable points, to roll up and leave the body as an isolated vortex.
At the Mathematicians' Congress in Heidelberg then, Sommerfeld then heard Felix Klein
saying to Prandtl: "Your talk was the most beautiful one of the whole congress."
It is characteristic for the plenty of ingenious ideas Prandtl had at that time that, in
addition to the boundary-layer theory just mentioned, he presented a paper at the same
Mathematicians' Congress that dealt with the area of the theory of elasticity. Since thattime, this paper is known to every theoretician in elasticity as Prandtl's analogy between
the torsion of a prismatic bar and the curvature of a soap film, which is formed on a holeof the same cross section as the bar under pressure from one side. This equivalence hasoften been used for the solution of torsion problems in experiments."
On the latter problem, two articles have been published in print [24, 40].
The letter of appointment letter for the post of professor at Göttingen was already inPrandtl's hands, when the Heidelberg Congress took place. Its exact wording is on
record:"The Minister for Education in Spiritual Matters and Medicine, Berlin, 31 July.
In pursuance of the negotiations conducted with you upon my commission, I herewith
appoint you with the most supreme authorisation of His Majesty the Emperor and theKing, from the 1st of September of this year onwards, to the post of ausserordentlicher
Professor in the Faculty of Philosophy at the University in Göttingen, and bestow youwith the duties of giving lectures and tutorials in technical physics and agricultural
machines that were hitherto held by Professor Lorenz within the purview of theExtraordnariat. Concurrently, I transfer to you the directorship of the Division ofTechnical Physics belonging to the Institute of Physics. I request you to take over yournew position before the beginning of the next semester, and send to the Dean of theFaculty by return of post the list of lectures to be announced for the next semester.
Instead of your present service pay, I approve from 1 September of this year, an annual
salary of4000 M(arks)
to be paid to you and an annual housing allowance of
540 M(arks)"

31

For the month of September, Prandtl, arranged for his deputisation, On 1 October, hetook over the work of his new appointment at the university. For the same autumn
semester 1904, Felix Klein had also asserted the appointment of Carl Runge to a positionin Göttingen. Just like Prandtl, he was eagerly looking forward to this move. In June
1904, Felix Klein had personally asked Carl Runge, if he would also like to come over toGöttingen. When Runge talked to Ministerialdirektor Althoff in Berlin about this subject,
all his demands were met to his joy. The new position was upgraded to the post of anordentlicher professor with corresponding increase in salary. Runge had received calls
for positions in other places, such as Marburg, Danzig, and Aachen, but none of these
universities could offer the pay he asked for. His chair, designated as "Chair for Applied
Mathematics" (Lehrstuhl für angewandte Mathematik), was the first in Germany for thissubject. Prandtl had been appointed Professor for Applied Mechanics. Both of them
moved into an old venerable institute building on the Prinzenstrasse, into the so-called
Michaelishaus, in which Karl Friedrich Gauss and Wilhelm Eduard Weber formerly had
made their first experiments with electromagnetic telegraphy.
Iris Runge writes [44]:"The rather small angular rooms, the worn out floor in the hall
entrance and stairs reminded you of the age of the building that dated back to the 18th
century. Yet, everything was bright and new, although furnished in a simple andfunctional manner.
When Runge came to Göttingen, Klein asked him and Prandtl to conduct a joint seminaron problems in electrical engineering.
At the time of registration, the science students were given a study guide prepared by
Klein that had the title: "Suggestions and explanations for students of mathematics andphysics". Its aim was to lead the young people to the important tasks without any detour.
Anyway, these years saw a unique collaboration of all those who were involved asteachers in the vast structure of the knowledge of nature. All parties involved werecooperating, starting from those representing practical applications, the group to which
Prandtl and his mechanical engineering laboratory belonged - his subject was named bysome colleagues as Fakultät Schmieröl ("Faculty of Lubricating Oil")- right up to theguardians of the pure heights of mathematical theory."
The most renowned professor among the mathematicians was David Hilbert. Klein had
been successful in his efforts to bring him (Hilbert) to Göttingen, where he stayed until
the end of his life, and rejected an offer from Berlin in 1902. Klein's suggestion to extend
the science division of the Philosophische Fakultät (Faculty of Philosophy) was in linewith Hilbert's thinking, and provided a broad base for students from all over the world.
Runge and Prandtl, whose friendship had its roots already in their time at Hannover, wereparticularly close to each other. In Göttingen, they moved even closer to each other bothin spatial and professional respect, which was a very fortunate constellation. But it was
the free atmosphere at work in Göttingen that brought Prandtl's originality in engineering
mathematics into full bloom. The union of Prandtl's and Runge's institutes often provided

32

the opportunity for stimulating discussions, which was conducive for the origin anddevelopment of new ideas.
Prandtl, looking for further insights in his special field of research in fluid flows, now
mainly dealt with the area of gas flow. He got good chances for research work in his
institute. Already in 1898, Klein had founded the Göttinger Vereinigung zur Förderung
der angewandten Mathematik und Physik (The Göttingen Society for Promotion ofApplied Mathematics and Physics) together with interested industrial magnates and some
professors from Göttingen. Substantial financial aid from the industrial magnates hadenabled him to take up new institute projects, e.g., the Physikalische Institut on
Bunsenstrasse in 1905. This offered more space in the old Physikalisches Institut on the
Prinzenstrasse for the new Dozents, and Prandtl could extend the existing facilities
through a closed-circuit water tunnel for flow visualization.
As explained in the preceding text, I wish to emphasise at this stage that Prandtl went
ahead with his research in fluid flows as a purely scientific piece of work. After he had
solved the practical problem for MAN, he continued research in this area in his own
interest and for the sake of gaining knowledge. In the beginning, he had no idea that his
science would have a bright future.
In 1906, again with the cooperation of Ministerialdirektor Althoff, a new society was
founded: the Motorluftschiff-Studiengesellschaft (Society for the Study of Powered
Airships) with the essential goal to promote the development of the Parseval airship.
Prandtl was chosen as a member of the technical committee. Klein suggested drawing
plans for a laboratory for model studies in order to establish a superb scientific working
atmosphere for conducting tests and preliminary studies. He commissioned Prandtl withthis task. Thus, the impulse for a development that corresponded to his inclinations andwishes came in a certain sense from outside. Soon, the building plan blue prints wereready and the preliminary work started in the beginning of 1907. By the way, Prandtl
received an offer for an appointment to the TH Stuttgart. In a letter to Ministerialdirektor
Althoff, he described his situation in respect to his teaching duties and disclosed to him
his standpoint towards the offer.
"30 March 1907
To His Excellency Herr Ministerialdirektor
Dr. Althoff, Berlin, Ministry for Education
I have the honor to inform Your Excellency that, yesterday, I received a letter dated 26
March from the Württemberg Ministry of Education in which an offer of the position ofan Ordentlicher Professor for Technical Mechanics at the TH Stuttgart has been made tome.
Although this offer is very attractive to me, there are reasons for me to give serious
consideration to remain in Göttingen. Of course, I am not without wishes. I am quite
happy with my Institut except for the very stringent budget that has not been raised up to33

now. But thanks to the aid of the Göttinger Vereinigung (Göttingen Society), which has
kept the Institut from drowning, this does not cause me much concern.
I am less happy with my present teaching activities, as despite all my efforts, it has notbeen possible for me to get a larger circle of students interested in my efforts. The reason,
partly, is that the subject is put aside as an unnecessary minor subject, since it is handled
only by an Extraordinariat, that has little or no participation in conducting examinations.
Therefore, my wishes primarily concern the measures to elevate the standing of mysubject.
One request that I address especially to your Excellency, is to upgrade my teachingposition to an Ordinariat, or, if this is not possible, to grant me the position of a personal
Ordinariat. My personal position in this matter remains the same as 3 years ago, I gaveup the chair of an Ordinariat in Hannover gladly, and even now, I do not ask for aposition with voting rights in the Fakultät. However, I think I owe it to the standing of
the chair that I am holding, to raise this request.
A second measure to reach this goal of being taken as a member of the examinationcommission for Applied Mathematics (examination for teachers' qualification) has
already been initiated. Moreover, I intend to place a third, which refer to the changes on
the award of a Doctor's degree (Promotion) in physics before the Fakultät in Göttingen.
Besides these things, there is another request on my mind: I am needed in Göttingen tohandle heterogeneous matters, among which the subject of agricultural machinery is very
remote from my scientific interests. Transferring the subject of agricultural machinery toa suitable Dozent, as I once reported to the minister, would relieve me of the burden of
the Division of Agriculture and at the same time be a scientific gain to me.
Since the Württemberg Ministry has informed me that that the matter is urgent, may I
kindly ask for your early reply.
Devoted L. Prandtl"
Prandtl rejected the offer for the post in Stuttgart, since his demands for Göttingen were
met and his professor's post was upgraded to that of a personal Ordinariat. They planneda laboratory him there. In autumn 1907, a closed circuit wind tunnel was built according
to Prandtl's specifications at the east of the Leinekanal on Hildebrandstrasse. The crosssectional dimensions of its test section were two metres by two metres. It was equippedwith a powerful blower for wind generation, and later on, this type was copied and built
abroad as the Göttingen-type wind tunnel. Independent of this, the engineer Alexandre
Gustave Eiffel had built an open-circuit wind tunnel in Paris almost at the same time.
This design was also developed further. Eiffel's experimental facility was primarily toserve a special goal, viz. to measure the wind pressure on the tower he had built.

34

Professor Ludwig Föppl writes: "Almost at the same time as the German wind tunnels
were built in Göttingen, the builder of the Eiffel Tower put up a similar wind tunnel inParis and got drag measurements conducted there. Therefore, it was possible to compare
the results of measurements obtained in Göttingen and Paris with each other. There was agood agreement between the two for most of the models. In contrast, for some models,
the results of the two measurements differed from each other significantly. Although themeasurements were repeated with great care both in Göttingen and in Paris, thedifferences in the drag coefficient remained the same."
After different conjectures on the physical reason for the discrepancies were put forth,
Prandtl succeeded in explaining the same in a surprisingly simple manner with the help of
his boundary-layer theory. The reason was that the airflow in the wind tunnels at
Göttingen and Paris was not identical. After the inclusion of a contraction, the airflow
available for measurements in the Göttingen wind tunnel was turbulence free, whereas it
was more turbulent in the Paris wind tunnel. Through carefully conceived experimentswith spheres, in which in one case vortices (characteristic of turbulence) were generated
by a mesh in the flow and in the other a tripping wire ring soldered onto the surface of thesphere disturbed the smooth flow, he could eliminate the discrepancy, and thus,
conclusively prove his thoughts [22].
"Prandtl was awarded the Benett prize for this impressive explanation of the controversial
question."
It was surprising again and again how many sided the problems were that he addressed.
At that time, with an agreement by the Motorluftschiff-Studiengesellschaft ("The Powered
Airship-Study Society"), he was also engaged in the design of a flying kite. The insights
he gained in his wind-tunnel studies, which provided results that enabled a drastic
reduction of the large energy losses incurred in flying in those days, promoted thedevelopment of flying objects. Models of airplanes, navigable airships, and wing profiles
were suspended in the wind tunnel and their drag was measured at different wind speeds.
The scientific evaluation of the precise measurements led to the development of thestreamline shape and form.
The switching on of the blower could be heard well in the surrounding neighbourhood; it
could not be kept a secret that unusual things were happening there on the
Hildebrandstrasse; but the new "Home of the Wind" (''Windheim'') belonged to theprogressive side of Göttingen. Considering that Otto Lilienthal, with his own design of aglider resembling a flying bird, started as the first flying human being in 1891, and that in1903, the American Wright Brothers ventured their first powered flight with their twindeck airplane, whose flight characteristics were only tested sparingly, it has to be
accepted that the science of flight research with its results taken for granted today, wastotally new at that time and attracted much public attention.
Moreover, the flight with airships brought much attention and appreciation, since it was
clear that a vehicle lighter than air had to prove itself in flight.

35

On 2 July 1900, when Graf Zeppelin succeeded in his maiden voyage on the Lake ofConstance (Bodensee) with his manoeuvrable airship, a reporter Eugen Wolf, wrote thefollowing enthusiastic article in the periodical, Die Woche,: "Christoph(er) Columbus
could not have experienced more intensely the feeling of being blessed when the cry"Land" fell on his ears than all those who were possessed by the dashing cavalry general
Graf (Count) Zeppelin, when finally, the majestic sleek air vehicle, that lent a feeling ofsafety in all its parts, obeyed a light pressure on the lever by its pilot, raised itself slowly
and silently from its parking place, and took a course through the air like a celestialapparition."
As against this, the very first trials of the Wright brothers to overcome earth's gravity by
motor power bore a closer resemblance, not to the weightless flight of a migratory bird,
but to a hen fluttering her wings. At its first flight, the powered airplane glided for 12
seconds over the ground before its skids touched the ground after 50 metres. The
spectators who had assembled together for this demonstration did not stare into the sky,
but had to crouch onto the ground in order to be a witness to the first powered flight. This
was the only stance that permitted them to judge whether the airplane had taken off theground. After persistent repeated trials these two aircraft technicians did succeed in flying
higher and more often.
In 1908, Orville and Wilbur Wright carried out several times in France, Germany andEngland successful demonstrations of their flying machines that had been improved in
the meantime. Airspace had thus been conquered. It was now the task of the
aerodynamicist to achieve stability and flightworthiness for the flying machines (objects).
Soon, scientific workers (wissenschaftliche Mitarbeiter) came together in the laboratory.
A few names are known to me: I wish to mention Th. von Karman first. His path ofstudies led him to Göttingen as early as 1906. In 1907, Dipl.-Ing. Georg Fuhrmann was
hired, who then worked in building up the laboratory. Dipl.-Ing. Otto Föppl joined in
1909. In 1911 and 1912, two further helping hands came in: Dipl.-Ing. A. Betz and Dr.Ing. C. Wieselsberger.
The Hungarian mechanical engineer Theodore von Karman wrote to Prandtl in 1906
asking if he could work with him as a doctoral candidate in the field of mechanics.
"8 September 1906, Budapest
Respected Herr Professor!
According to the instructions of the local Technische Hochschule I intend to spend thenext semester at the University in Göttingen and work during my stay in the areas oftechnical mechanics and heat. My task is to gain deeper scientific insight into thesemathematical subjects that serve in technical education, and in particular, in the trainingof mechanical engineers, as a preparation and foundation for the purely technicaldisciplines. . . .

36

I am convinced I can fulfil the task best, if I place myself completely under yourguidance.
Your devoted Theodor Karman"
Karman was a highly successful student of Prandtl (he got his doctor's degree working
with Prandtl in 1908) and became a professor at the Technische Hochschule in Aachen in1913. Under his direction, a wind tunnel according to the well-known design in
Göttingen was built as early as in the beginning of 1914. In 1929 he accepted an offerfrom America to be the director of a research laboratory in aeronautics in Pasadena. He
was unsettled by the political development in Germany and could forsee where the ideasof the NAZIs (Nationalsozialisten") would lead to, which would hit him especially hard
as a Jew. In America he found the very best conditions for work. Through his innovative
spirit, he helped American aeronautical research to attain lofty heights for which
generous financial support was available.
Karman did not let his connections with his former teacher in Göttingen snap, as long as
he stayed in Germany. Both the scientists did research on turbulent flows and exchanged
their results.
In his biography "The Wind and Beyond" Karman writes [15]: "In my opinion Prandtl
unraveled the puzzle of some natural phenomena of tremendous basic importance andwas deserving of a Nobel Prize."
Prandtl had settled down well in Göttingen. He regularly met for lunch with a group ofcheerful young Dozents who were still bachelors. Members of this group were: Karl
Schwarzschild, astronomer, Professor Max Pohlenz, philologist of old languages, and thephilologist Jakob Wackernagel. The intellectual exchange of thoughts was many-sided.
Soon, the bonds of friendship between him and the two years older Karl Schwarzschild, avery amiable person, became closer. His observatory often served as the social meeting
place for many of his friends including Carl Runge. His almost playful ways to deal withmathematics inspired him to entertain his friends with amusing experiments.
Just like Prandtl, Schwarzschild was also enthusiastic about the balloon flights that were
within reach. The Niedersächsische Verein für Luftfahrt (Lower Saxony Society for
Aeronautics) that had been founded enabled its members to arrange for a balloon flight in
Göttingen. The balloon, which was made in a balloon factory in Augsburg from "double
Perkal" material, had a diameter of 14 metres when filled. It was called Segler (sailor).
The balloon was anchored in a field near the gas works, filled with gas until it took aspherical shape, and was then ready for its journey in the air. Later, as a child, I haveonce been a witness to such a balloon take-off. There was much waiting time going alongwith it, but the excitement grew in the very moment when its anchors could be loosened
and the balloon levitated, remaining within sight for a long time.

37

The Board of Governors of the Society had laid down regulations for those aspiring toobtain a licence for flying balloons. It had joined the Deutscher Luftschifferverband(German Airship Society) as a corporate member and followed the guidelines set out by
the society, e.g., the certificate of proficiency in reading instruments and judging
atmospheric conditions (weather, solar radiation, and cloud formation). Anotherrequirement was: "The Board of Governors conducts an examination through anespecially constituted committee as to whether the aspirant can supervise the preparationand filling of the balloon without the help of an expert and is capable of doing the needful
operations by himself." The payment conditions for accompanying persons were also laiddown.
A note in the newspaper Göttinger Tageblatt of 10 January 1908 indicates that Prandtl
travelled as a passenger in a balloon:"In the balloon from Göttingen to Berlin
As reported earlier, four Dozents of the Göttingen University, Herr Professor Prandtl andDrs. Linke, Pütter and Bestelmeyer, recently flew in a balloon to Berlin. They took off inthe balloon Segler at nine in the morning and landed, after a seven-hour flight without
untoward incidents, at four in the afternoon on the shores of the Müggel Lake, not far
from Rahnsdorf. The airship was piloted by Dr. Linke. The balloon Segler is a vehicle
with an air capacity of 1400 cubic metres. The Verein für Luftschiffahrt (Airship Society)held its annual general meeting on the same day in Berlin. When the gentlemen took off,
the wind direction raised hope for a punctual landing in Berlin enabling them toparticipate in the meeting. However, since they had only a free balloon at their disposal
and not a manoeuvrable airship, these hopes stood on rather shaky ground. Therefore, thefour scholars were all the more proud that they could be at the meeting in time."
After a few short trial flights under instruction, Prandtl obtained a licence for piloting aballoon all by himself. On 15 August 1909, he wrote to his fiancée Gertrud: "You may
congratulate a newly baked balloon pilot, I passed the examination yesterday."He undertook several flights as a balloon pilot that made him extraordinarily happy. The
opportunity to observe the natural wind currents and feel the same as a fundamental force
when flying, was a unique experience. He derived great pleasure from being able toobserve with keen attention the cloud formation and the landscape spreading out below
him. On his balloon flights, Schwarzschild conducted astronomical position
determination with a surveying sextant. The creative imagination of the scientists was
stimulated by these undertakings again and again.
In 1909, Schwarzschild got an offer from Potsdam and became the Director of the local
Astrophysical Observatory. He left the familiar Göttingen with all his good friends.
In contrast, Prandtl's steady rise took place within the Göttingen framework.

38

On 11 January 1909 he got the following order from the Ministry: "In addition to thecommission to teach that you already have I authorise you (Euer Hochwohlgeboren!?),from the next semester onwards, to represent the entire field of scientific aeronautics alsoin lectures and tutorials. ..."
There was the following announcement as a news item in a newspaper: "The Minister of
Education has granted Dr. Prandtl of Göttingen a commission to teach aerodynamics. As
far as we are informed, this may be the first professor for aeronautics."
His course of lectures was divided into six sections:
1. Aerostatics: On the equilibrium of the entire atmosphere and the fundamentals ofdynamic meteorology
2. Aerodynamics: General laws of fluid motion
3. Equilibrium of flying kites and gliders
4. Propulsion by airscrews
5. Stability of balloons and flying machines
6. On navigation - terrestrial and astronomical determination of position, radius of action
under wind influence.
In its issue of 15 April 1909, the periodical Berliner Illustrierte Zeitung approached
Prandtl with the following request:
We read in the newspapers that you will shortly be heading the first college ofaeronautics at the University in Göttingen and plan to combine your lectures(Vorfuehrungen!! sind gemeint Vorlesungen??) with practical demonstrations. We
request you to please allow our draughtsman to draw such a lecture in which experiments
are conducted with models, and hope for your agreement."
Even the French press reported about the new chair, and in the English Times of 7 April
1909, the aerodynamicist F.W. Lanchester published an article on the problems of airshiptransport from which I quote a paragraph:"In Germany, a chair of aerodynamics has been founded at Göttingen, appropriately filled
by a very able physicist, Professor Prandtl, whose work is well known and who continues
to hold the chair of applied mechanics at the Göttingen University in addition to his more
recent appointment.
The aerodynamics laboratory at Göttingen had already been built and equipped by private
enterprise before the new chair was founded, and it is probably the best thing of its kindin the world."

39

4. Engagement and marriage
During all these years Prandtl's relationship with the Föppl family was very active. They
repeatedly met each other during the holiday season, since Prandtl did not miss paying avisit to his respected teacher whenever he was in Munich. There might have been a secretattraction for him to pay these visits---that is the chance to meet the meanwhile grown up
daughter Gertrud at the Föppls, who modestly withdrew as soon as the father came to beengaged in conversation with the visitor.
The exchange of thoughts and opinions between the older and the much younger
colleague was very stimulating. They discussed scientific subjects that could be thought
out afresh again and again; while this brought their intellectual world closer together, themutual trust between them kept growing. They also wanted to talk over mattersconcerning personnel and new appointments to positions at technical universities.
Besides communications on family matters, many of August Föppl's letters containsuggestions regarding calls to chairs and scientific work that cannot be given a place inthe text I am writing now. I wish to include excerpts from private communications only.
From the letters of August Föppl:19 November 1903:''All of us are well. Recently, my daughter" (Gertrud) "was on a visit to Hannover for a
few weeks and she saw you from a distance, from a gallery at a Commerse."
1 January 1906:
My wife and I would be delighted if you came down to lunch with us at 12.45 on
Thursday 4 January (entirely within the family, so please come in travel suit). On 3
January, I start my lectures again; so you would meet me also on 3, 4, 5 January after thelecture at 10 o'clock in the laboratory."
In 1908, August Föppl wrote to Prandtl with a personal request:
22 July 1908:
My younger son Ludwig has studied mechanical engineering for two years and has now
reached the stage of Vorprüfung (preliminary examination). There is no doubt that hewill pass the examination with the best grades. However, it has become clear now that heis indeed talented in the mathematical subjects and is very happy doing them, but does
not want to know much about machine design. I intend to put him through studying
mathematics provisionally for one year, and that in Göttingen. When the year is over, hecan decide for himself, whether he wants to pursue engineering studies or entirely changeover to mathematics.
My request to you is to draw up a time-table for my son. You will know the lectures in
Göttingen that are especially worthy of recommendation to a young diligent and talented
man.

40

Thanking you very much in anticipation for the information (if it is not conveyed orally
in person which I would prefer),
your much devoted August Föppl."
In this summer, they also met during the holidays which Prandtl always spent in South
Germany. Since 1894, the Föppl family had owned a holiday home on the lake
Starnberger See so that guests could be comfortably accommodated there in the
countryside during the holiday season. As he would often do, Prandtl took a short trip
from Munich to Starnberger See, met the family in Ammerland, and had the opportunity
to advise Ludwig at length on changing the subject of study.
With the beginning of the autumn semester of 1908, the student from Munich (Ludwig
Föppl) started attending the mathematics lectures in Göttingen. He attended the collegesof David Hilbert and Felix Klein, whose fame attracted many students from elsewhere. It
was an advantage for him that he could also participate in that seminar on mechanics thatwas referred to earlier and held by Klein, Prandtl, and Runge together.
Thus there grew a new closer relationship between the Föppl family and Ludwig Prandtl.
The professor in Göttingen also took personal care of the student son of his former
teacher.
Moreover, Prandtl always asked him, how the other members of the family in Munich
were doing. When Ludwig Föppl informed him in December 1908 that his sister Gertrud
would be engaged soon, the young scholar could not hide a certain excitement. My uncle
Ludwig told me later that Prandtl stared very sadly into space, when he heard this news.
On 31 December 1908, he sent his colleague Föppl his best wishes for the New Year
together with a congratulatory message on the engagement of Fräulein Gertrud.
3 January 1909, letter from August Föppl:"Many thanks for your kind letter for the New Year. One of the greetings contained
therein, however, has missed its objective. The engagement of my daughter Gertrud was
broken after a short period of life." (It is reasonable to suppose that Prandtl did not takethe news of the turn of events indifferently.)
August Föppl then continued: "I thank you very much for the kind acceptance andsupport you have given to my son Ludwig. Now you will get my son Otto to Göttingen,
too! In the beginning, I did not like it very much that he wanted to quit his post in Gotha
so soon. I value continuity and perseverance in leading one's life. I hope that he will
come up to your expectations."
Engineer Otto Föppl, the elder son, also came to Prandtl to Göttingen. He was an
Assistent to the young aerodynamicist in the Modellversuchsanstalt .

41

Soon, even for the daughter Gertrud the town of Göttingen was destined to gain special
significance in a more eventful manner than for her brothers. And we will now relate how
Gertrud's path in life led her from Munich to this town.
On Easter 1909, Prandtl made up his mind to ask Gertrud to marry him.
In his memoirs, Ludwig Föppl has noted down the following:"Prandtl had planned avacation trip to the lake Gardasee and Bozen over the Easter holidays. As he often used
to do on such occasions, he stopped over in Munich to visit us and conversed with myelder sister Gertrud. Soon thereafter, she got a proposal of marriage from Prandtl in a
letter he sent from Riva:“Riva, 20 April 1909
Respected Fräulein! In the solitude of the mountains, my decision has matured to ask you
a question I have been carrying along with me for long.
This news set off a feeling of great joy in me, since I knew my sister would not be in
better hands with any other man. My parents also thought likewise. Gertrud's decision toaccept the proposal of marriage was not long to come and she wrote her decision to
Prandtl. Since he had planned to travel on to Bozen, he had requested her to send him her
reply by poste restante. He had also told her, how long he intended to stay in Riva, but
due to some absent-mindedness, he had not indicated the name of the hotel, where he wasstaying. Since Gertrud replied without any delay, she sent the same to Riva to be held
poste restante. Meanwhile, Prandtl thought that her letter would reach him at the hotel, if
the reply was to follow without delay. After his arrival in Bozen, he waited in vain for theposte restante reply from Munich.
For Gertrud, it was a week of anxiety during which there was no news from Prandtl.
When I had to return to Göttingen at the end of April in order to be there in time for the
beginning of the summer semester, a reply to Gertrud's letter had not yet arrived. I
comforted her saying that I would ask immediately after my arrival in Göttingen, if
Prandtl had already returned from his trip. I was told he had not yet returned, but was
expected soon. I immediately informed Gertrud accordingly. After finding out the date of
his return, I went to his home at the address Kirchweg 1a in the evening and, after an
exchange of courtesies, I hesitatingly asked him, if he had not received the letter that mysister had sent to him poste restante to Riva. Totally surprised, it came out of him:'To
Riva? Every day, I inquired about a letter from her at the post office in Bozen and,
finally, I had to return to Göttingen.' After this error was explained, there was joy on all
sides and we greeted each other as brothers-in-law. The same night, I sent a telegram toGertrud assuring her that everything was in order, and on the day following, I wrote her
in a letter what had happened."
The parents Föppl welcomed the alliance whole heartedly.
August Föppl on 10 May 1909:

42

"Dear Colleague!
I am very happy that you and my daughter have agreed to enter into the bond of marriage.
I give you my blessings from the bottom of my heart. I have always highly admired you,not only as a scholar but also as a human being, and I do not know of anyone, whomwould be more welcome to me as a son-in-law. Since we will come closer as yet, therules of grammar demand that we address each other as "Du" in the future, and I use it
straightaway. Gertrud has always been a good and loving daughter to me. I will miss hervery much. We hope to see you here with our other sons over Pentecost (Whit Sunday).
We can come to an agreement on all details then.
Your old teacher and new father-in-law."
Frau Emilie Föppl wrote:"Like my husband, I also want to introduce straightaway the familiar form "Du" byheartily welcoming you as my dear son. I am very happy about this alliance. For many
years, I have had a special affection for you and I believe devoutly that my child will findher happiness in life with you. Since Gertrud has been brought up to seek that profoundhappiness in faithful fulfillment of duties at home, I hope she will be a partner of the kind
you wish.
May the blessing of God be with you on your way together
Hearty greetings! Your faithful mother E. Föppl."2
From Prandtl's letters during the engagement period:
5 May 1909:
My youth was bleary due to the misfortune that befell my parents. But my equanimity
helped me tide over even the saddest times without my entirely losing my vitality. Lateron, I was extraordinarily lucky, indeed. If, by a grant of destiny, we find ourselves inhappy accord with each other concurring harmoniously without break, it will then havealso brought me much more than what it could have ever taken away from me."9 May 1909:
Unfortunately, we men can almost never return to our wives what they give us in
devotional love. The wife totally dedicates herself to domestic matters for the sake of her
husband---in contrast, she has to share him with his professional interests.
2

It should be mentioned in this context that the account on the story of Prandtl's marriage given
as incidental by Professor Th. von Karman in his book "The Wind and Beyond" (in German "Die
Wirbelstrasse", Hoffmann und Kampe Verlag, Hamburg, 1968) does not correspond to thisaccount.

43

With me, things are particularly bad: You will have to compete with two rivals. One ofthem is a dignified lady, who keeps, however, her devotees stick to her path with analmost divine power. The other, although still young as a bud, casts her net withseductive attraction on anyone susceptible to fall for her beauty. Shall I name these? One
is science, and the other is the motion of airships.
In this semester, I am more up to my ears in work than before! There is the setting up of
my Modellversuchsanstalt (Laboratory for Model Experiments), which was already the
subject of a debate in the English Parliament , the lecture course on airship motion forwhich, of course, I have to work out new material, and different lectures that I haveagreed to give. One lecture is to be given at the General Meeting of the Verein Deutscher
Ingenieure (VDI, German Society of Engineers), another at the Frankfurt fair (ILA Internationale Luftfahrtausstellung - International Aeronautics Fair). In the latter, I will
participate in two capacities, as an exhibitor on the one hand, and as the head of the prize
contestants on the other.
If I knew, where I could get the time, I would also like to work on building a flying
machine. But for various reasons I will keep away from this plan for the present.
You ask me what I normally do on Sundays. The answer: writing letters, going throughliterature. After lunch at 'Englischer Hof ' together with a group young Dozents, wemostly take a walk in their company that may range from a simple coffee stroll to aneighboring village up to a trip to somewhere in the Mittelgebirge, depending uponmood and weather. Today, for instance, we walked through the beautiful valleys withblossoming cherry trees all the way up to the proud Burg Hanstein. You will certainly
like this very much in Göttingen. You are close to nature everywhere so that you can live,
as if you were in the countryside, since the new districts of the city have been laid out asa garden city."
2 July 1909 - Prandtl sends his bride suggestions for an apartment to live in: "1. PrinzAlbrechtstrasse 20, first floor, preferred pretty location. Bordering at the back with theplot of the observatory" (his friend Schwarzschild was working there at that time)--"twelve minutes to the Institut, nine to the market."He also mentions an apartment situated farther away and includes the following balance
sheet: "Covering the distance to the Institut twice a day means 40 minutes more to walk,with 288 working days per year that would amount to eight full days and nights. When I
weigh the pros and the cons against each other, I come to no conclusion, because theadvantages and the disadvantages balance each other. I hope things are better with you
and you clearly tend to one of these."
Obviously, Gertrud made her choice from a distance and decided in favor of theapartment on Prinz-Albrecht-Strasse.
10 July 1909:

44

"Today, I sent the sketches of the furniture. I do not like any of the different buffets I
found, so I sat down and made a design myself."
The drawing is still there, and I unmistakably recognized the same as the buffet that wasin my parents' dining room
All these letters show, how much he invested in errands, writing and thoughts on these
private matters in spite of the heavy load of work. After all, this was important for him.
Prandtl's description of moving into the new apartment: “Moving in went on as follows:
Getting up at half past five - from six to eight I had one filling of the balloon (unpowered
balloon)---the packer came at nine---I helped him until eleven. From eleven to one, I had
to hold a seminar. Lunch - loading of the furniture from two to half past three,transportation from half past three to four, arranging in the new apartment from four tohalf past five. Now a pause for rest. At nine, for a finish, one meeting of the seminarboard of directors."
The marriage was waiting just around the corner. An agreement had been reached in
respect of religion that Prandtl would remain in the Catholic church but Gertrud's
protestant ancestry would prescribe the formalities for the marriage. On 11 September
1909, Ludwig Prandtl and Gertrud Föppl married in Munich according to evangelicalformalities. The marriage festivities were held at the Föppls' house, Hess-Strasse 10.
My aunt, the ten years younger sister, told me in her old age that she could come down toGertrud's wedding in spite of staying at a Swiss boarding home, where she was learning
French. Contrary to her grown up brothers, she considered the new brother-in-law as amember of her father's generation, since they had moved with each other as colleagues.
The nature of the relationship between the two scientists, however, changed slowly. The
father-in-law kept himself more to talking about family matters---he was rarely inclined
to engage in discussion about technical subjects.
Three weeks later, there was a second marriage celebrated within the Föppl family. The
elder son Otto married the daughter of a colleague in Munich. This young couple also
moved to Göttingen. Otto Föppl, who had submitted part of his work done in Göttingen
on the subject "Forces due to wind on plane and cambered plates" as a dissertation [8],later became a professor for strength of materials in Braunschweig.
When my mother came to Göttingen at the end of September 1909, she was enchanted by
the life in this small town and she experienced no difficulty in feeling at home here soon.
They returned from their honeymoon which had taken them to the lake Gardasee. At therailway station in Göttingen, they boarded an open coach that moved on at a leisurely
pace through the town and brought them to Prinz-Albrecht-Strasse (today renamed as
Kepplerstrasse). On the way, my father showed his young wife some important buildings,
like the Physikalische Institut looking over the river Leine and the university library. At

45this point, the bend to the Hauptstrasse had already been reached and the route followed
Weender Strasse over a certain stretch in the direction of Quentins Eck. The lady from
Munich was very amused that this short distance from the Auditorium to the Markt was
Göttingen's main thoroughfare. My father also gave some suggestions for shopping here
and there. In passing, they saw the Rathaus (town hall) and the Gänselieselbrunnen (thewell-known fountain in the town of Göttingen). At the Markt, the small steed drew thelight carriage around the corner and went up along the Lange Geismarstrasse and theKurze Geismarstrasse through the Geismartor (Geismar gate), from where the mighty
stone lions looked down in a sphinx-like manner. Shortly thereafter, the ride ended,
Prinz-Albrecht-Strasse 20 being the end-point of the long journey. The next move wasinto the six-room house that my father had rented in the meantime. He had followed theadvice of relatives and had hired the services of a housemaid, who received them andhelped unpacking.
The next morning, my mother wanted to look around the town and do some shopping.
When she entered a shop on Weender Strasse, she was served with extraordinary
attention. And then she heard the shop assistant say: "Yes, please, Frau Professor, may
we send you these things to your apartment?" She (my mother) could only reply quickly
by asking: "How do you know me?" "Yes, we did see you yesterday afternoon goingalong here in the coach with Herr Professor." To some extent, my mother felt enchanted
and at the same time amused. In this town thorough which she had just passed as a
stranger, she was already known. In Munich, she had walked through the streets without
drawing attention. Here, in this small university town, she was already expected and was
paid the attention accorded to a Frau Professor. Without a foreboding, the couple in thecoach had probably drawn the attention of many eyes.
My father, brown-haired, with a full black beard, looked serious and mature. Next to him,
my mother with her blond hair pinned up, looked very young and tender. At that time,
she was 27 years old.
Very soon, she got used to her new role that was assigned to her rather suddenly throughthe marriage. When she was awakened in the morning by a knock on the door with thewords: "Frau Professor, hot water is ready", she had to think once and establish withastonishment: "That is me, this Frau Professor!"Once she said to me: "It is certainly very nice, if you share the experience of success withyour husband all the way, help him here and there and having the joy to rise with him up
step by step. I had experienced things that were undeservingly kind." She was given a
position commensurate with the high esteem her husband enjoyed and was always treatedas a respected person.
Although she had spent a few months looking forward to this new world that she thought
she knew a little from the accounts related by her brothers and her fiance, everythingactually was surprisingly different. She was soon stretched to the full in the new sphere oflife. Since her husband did not have a secretary of his own, it turned out that she took
over the work of typing for him. Both had learned the same shorthand, the Gabelsberger,

46

which eased their cooperation. This gave her an opportunity to gain some access to his
intellectual world and, above all, an insight into his circle of people. Her clear anddecisive way often was a fortunate supplement to his nature, since problems arose forhim, as he was thinking over and over again even on trivial details, carefully weighing
their pros and cons against each other. As far as day-to-day matters were concerned, his
thoroughness, with which he always patiently explained to us his point of view andreflected aloud on the various alternatives, had something of a touching nature. In
contrast, my mother found it easy to come to a quick decision and it was comfortingwhen decisions on matters arising in day-to-day life could be taken without
procrastination. A scene that is deeply engrained in my memory due to its repeatedoccurrence, illustrates this point. He opened the day's mail at breakfast and got absorbed
in reading them. Then he suddenly stood up, now in a hurry. Yet he looked out of thewindows on different sides of our apartment to observe the sky, read the temperaturefrom the external thermometer, and deliberated on the question, which overcoat to put on.
The decision was even more difficult, if suspicious looking clouds covered the sky:Should he take an umbrella with him? He asked for my mother's advice. She replied withno hesitation. Without casting even a quick glance through the window, she said withcheerful optimism: "You will not need an umbrella." The reply was: "That's fine, it isyour responsibility", and the black object was left back hanging on its hook at home.
The couple loved to take long walks. On Saturday afternoons as well as on Sundays, theywalked through the near woods, sometimes going as far as the neighboring villages.
There is a note indicating that a first social get-together at the Prinz-Albrecht-Strasse washeld on 7 December 1910. The young wife had to prove herself at hosting after they had
been invited one after the other by the families of their colleagues during their first yearof marriage. My father was very happy to be able to receive his colleagues at his own
home after so many years in Göttingen as a bachelor. The Hilbert couple, Geheimrat
Klein and his wife, Professor Runge, Professor Wiechert, Professor Simon, and others, allcame for dinner. To judge from the expressions of content by my father, it must havebeen a nice evening.
But my mother understood very well that very frequent get-togethers in the evening
would rob her husband of the hours he normally used for work at night. Therefore, theygenerally avoided entering into large-scale social commitments. In contrast, Gertrud's
brothers often came to their home for a snug Sunday lunch.
For the rest, the couple enjoyed being together all by themselves at home. One of therooms was furnished as a music salon. On its window side, there stood a Bechstein pianothat my father had bought when moving in. Hardly did a day pass without the piano beingbrought to sound. Even in his old days, he felt the urgent need to sit at the piano at least
once a day to get absorbed in the world of tones. Without needing the help of any score in
front of him, he then played on the keys, drawing energetically from the rich well of his
creative imagination. His sources of inspiration were the (musical) ideas of Bach or
Mozart, Beethoven and Brahms, which he changed and developed into his own
structures. All of his improvisations probably resembled each other in style, but his

47

musical ideas were so rich that they sounded new and original, never being repeated.
Once, when we expressed our admiration, he only replied: "Oh, I have stolen the themefrom Haydn, it is not mine." But, of course, he could come up with his own theme that hedeveloped in the form of a fugue. He seemed to have an endless number of ways in mind
to express himself musically, to reflect his mood.
His piano playing meant a lot to us. We felt how much his music was an expression of his
entire personality. When he returned home late in the afternoon from his Institut and sat
at the piano, he sought relaxation in playing (the piano) and his imaginations spread out
an atmosphere of harmony, and the joy of life passed through a filter of art.
Later, when we had a little more understanding of music, we asked him among otherthings to try to compose a fugue with three voices. He pondered for a while and then, to
our astonishment, soon played a short composition with the usual interlacing of repeating
themes. It was a wonderful surprise to recognize the sovereignty with which his ability,
which we had put to test, had proven successful. Now it was our turn to think out a theme
for ourselves. For him, this was a new game again, and he did the task set in a cheerfulspirit.
I wish to relate here another occurrence that I remember from my mother's narrations.
Once, when my parents were visiting colleagues, who also had a piano at their home, thelady of the house related how sorry she felt that one of the keys of their piano had lost its
sound for some time; otherwise, she would have been glad to ask my father to play the
piano. He started playing and very soon he had to make the discovery that despite
energetic playing the key remained without generating any sound. While everyone hadgathered in the adjoining room and engaged in lively conversation, my father went to theother room, unnoticed by anyone, to look into the piano. He opened it with care and soon
found out the reason for the key remaining silent. A thimble had fallen between thestrings jamming the same. After gently removing the thimble, he sat at the piano andstarted playing powerfully from the low bass all the way up in rich harmonies. When thelady of the house opened the connecting door, he told her that she must have erred. All
keys were in order, he had just tried them out all. She looked at him unbelievingly andwanted to show him the particular key, and lo and behold, the key sounded correctly. The
lady now started protesting, saying that just the day before the key was without any
sound. Then my father said he had found something that he wanted to give her, andhanded over the thimble to the amusement of the rest who had gathered there. He was
now requested to play again. The happy appreciation of the small gathering was asufficient gesture of thanks for him.
Once in a while, my mother traveled to visit her parents, followed by trips to themountains for rest. The letters they wrote each other show how close they were to eachother.
Ludwig to Gertrud on 4 August 1912:

48

Now it is the end of the semester. I celebrated the same by sleeping long. My only
positive performance is this letter to you, while at least a dozen letters are waiting for ananswer! Monday 9 to 11 Sommerfeld, 11 to1 a double lecture squeezed in, afternoon
gymnastics, then dinner with Ludwig Föppl at our home. Karman joined us, they stayed
up to 11 o'clock and worked on an article. Otherwise, I would have written yesterday.
Yesterday was a big day here. The Zeppelin boat "Hansa" flew a round over Göttingen(the city civic administration and the Verein für Luftfahrt---Society for Aeronautics--paid for the round flight). The entire Göttingen population was either on its feet or on theroofs. We were on the veranda roof and saw it in its full magnificence. The bells wereringing, flags were hoisted on the towers, and jubilation was all around. It is a pity thatyou wern't here!"
A letter of Gertrud of 15 August 1912 ends as follows:"May you be well, my good, good husband. When I walk through the woods alone, I am
usually in conversation with you.
A thousand greetings. Yours Gertrud."Ludwig Föppl writes about these times:"After the teachers' examination in Munich, I went again at the start of the wintersemester of 1910 to Göttingen to work for my doctor's degree. The four and a half years
that followed gave me an opportunity to come in contact often with the newly married
couple Prandtl. I had a standing invitation to the Prandtls for lunch on Sundays. It is withpleasure that I recall these Sundays that passed by in harmony. Prandtl was no one who
despised a good meal.
He obviously enjoyed attending the Sunday barbeque and during the meal, he vented his
imagination of the possible tastes of the dishes on the table in different combinations.
After lunch that was followed by a short rest he sat at the piano, a beautiful Bechtstein,and played improvising. I enjoyed listening to him, sunk in a sofa, and admired his gift tolend musical expression to his mood of the moment without a score in front of him. Of
course, occasionally, the piano also had to serve experimental purposes, as for instancewhen he placed a newspaper on or under the strings and examined the effect of the sameon the sound. Since he had an ear for absolute pitch, he was able to tune the piano byhimself. Prandtl could be so deeply absorbed in his piano playing that he forgets
everything else. Piano playing was a source of spiritual regeneration for him.
An integral part of my Sunday visits to the Prandtls was a walk taken together in theafternoon walk. Usually, we took the route going up the Hainberg hill to the KaiserWilhelm-Park or to the Kehr where we had coffee. Prandtl's extremely alert mind tookdetailed note of changes, developments, and happenings in the surroundings on our way.
In spring, he could derive childlike pleasure from the blossoming of the flowers andlistened intently to the birds' singing. He followed the wind and the weather changes with
apt attention. With his comments, he gave further interesting explanations on his49

observations, so the walks were always very stimulating. I also came to know of hisstrong playing instinct. I remember that once in a cafe, he started building a tower fromthe crockery after finishing the coffee in order to examine the stability of the structure.
But it also happened now and then that one of the pieces broke, for which he then paid
the waitress with profuse apologies. These Sunday walks did all of us a lot of good.
Prandtl felt a strong need to take a brisk walk at least once a week. For him, it was acounterbalance to his normal way of life. This did also apply to the gymnastics with theprofessors, in which he took part every Saturday in the late afternoon.”
So, the precious years passed, during which Prandtl's esteem steadily grew, thanks to his
diligence and imaginative ideas.
Since in these years my own inclination to the subject of mechanics was clearly
manifested with both my doctor's dissertation and the Habilitation dealing with problems
in mechanics, frequent meetings with Prandtl and being with him were extraordinarily
fruitful for me in scientific respect. When I was stuck with some difficulty or the other, atalk with Prandtl often sufficed to help me tide over the same. He gave his help not only
to me as a brother-in-law, but also to all young people, who approached him with similar
requests. His benevolence and humane nature knew no limits. Therefore, he was verymuch liked by all, his students, Assistents and colleagues. Of course it also happened
occasionally that his benevolence was ripped off.
Also during the summer holidays, I often met Ludwig Prandtl, since we spent a few
weeks together in our parents' country house on the lake Starnberger See. He then tookwith him a file containing outstanding work and unanswered letters, which nailed him
down to his desk during bad weather. When the weather was good, he enjoyed spendingtime in our company in the garden, the charming landscape, and bathing in the lake. We
often stood together in the garden at a point with a beautiful view over the lake and thewhole Bavarian mountain chain, and Prandtl saw around, noted all details with attention
and liked to express himself in words over the same. In particular, the very impressive
atmosphere of the evening hours could make Prandtl react with much enthusiasm. Often,
when he saw the sky colored with extraordinary beauty, he called all of us and drew ourattention to the different coloring shades. One desire that always had a special meaning to
him was the weather observations. From our viewing point in the garden, thedevelopment of the weather could be seen well in advance. Prandtl often observed theapproach of thunderstorms and followed the origin and growth of cloud patterns with
their own peculiar characteristics. He often stayed there until the first rain drops fell. One
summer, when a newly planted pine-tree hedge just in front of our viewing point had
grown so tall that it obstructed the view into the distance, which had been possible so far,
we decided to build a small mound of gravel to provide an elevated platform for viewing.
We moved many wheelbarrow loads of gravel from a stone pit to the site. Prandtl helped
like a comrade at this physically strenuous work, although it was more difficult for him
than for us, the younger. He took part in all our enterprises, enjoyed every jest, and often
contributed to new ones. He readily adjusted himself to every situation and never spoiled
a sport, even if we sometimes made jokes about his clumsiness at physical work. In thesesituations, you could not notice the learned and renowned professor he was. He always

50

remained friendly and modest, as modesty actually is a sign of a high level of culture andeducation. He also played tennis with us on our tennis court, although he had no practicein that game and fast reaction was not in his prudent nature. But we were always happy,
when he played with us. There was much to laugh, for instance after a faulty stroke, when
he wanted to give a deep analysis of the stroke and we drew his attention to the difference
between theory and practice.
It is with very pleasant memories that I associate my walks with Prandtl in the
Ammerland region and its surroundings. His company at walks was always lovable andinteresting. Every puddle we passed by inspired him for experiments and he had to throwat least one stone to study the spreading of the waves. Once I went along the lake withhim, when there was a strong west wind, and we observed the group velocity of waves ofdifferent height. After drawing my attention to this phenomenon that was unknown to me
before, we sat on a bench, and he began instructing me through a few formulas that hewrote on a piece of paper. He derived the interference of two waves of almost the same
frequency, from which the relation follows that the group velocity is half the velocity ofthe single wave train. He, thus, coupled in his head his observations with the physical law
underlying the same.
This was precisely the surprising gift that he had: intellectual assimilation of observations
with the help of the basic laws of physics. Since this way of thinking had become an
integral part of his person ever since his youth and he used it instinctively at every step, it
made no particularly taxing demands of intellectual effort on him. The habit was
engrained so deeply in him that even at work it appeared, as if it were a product obtainedwith the same ease as in play. To me, it often appeared, as if he were in possession of an
infinite spring of knowledge in physics, from which he could draw with ease at any timeso that he could contribute to the problem under discussion. This would explain the hugevolume of his achievements in science as well as the broad span of his interests in all
branches of science. Whether it was a problem in physics or engineering, or in
astronomy, geology, or mechanics, he always sprang a surprise through his depth ofknowledge, often conversancy with details of special nature, and novel conclusions.
Repeatedly, he was engaged in conversations with different faculty colleagues on theirsubjects without needing any special explanations.
I had the fortune of having very close family ties with the two leading representatives in
the field of mechanics in Germany, my father August Föppl and my brother-in-law
Ludwig Prandtl. I have learned a lot from both, in science as well as at a humane level.
Although I stood only in the shadow of these two great men, I believe to be in a secondto-none position to judge on the work and the way of their lives. Over the years, I realised
to my surprise the generosity, with which mother nature distributes her gifts; although thetwo men worked in the same area of science, there was nothing common in their nature.
Of course, the two were of the same character in respect of excellence and reliability. It isalso superfluous to point out to their diligence, which ran as an unending stream throughthe course of their lives, since it is indispensable for success, even in science. However,they were different in their temperament and their way of work right from the very roots.
Even in their way of life, they were individuals cast in two entirely different moulds. You

51

can distinguish between two kinds of scientists: the classical and the romantic types, asWilhelm Oswald describes in his book, "Grosse Männer der Wissenschaft" ("Great Menof Science"). The latter is characterized as one gifted with genius, who accomplishes
great feats without any efforts right at the outset in his young years, whereas the classicaltype develops slowly and steadily and gains great success only after years of incessanttoil. If this classification were to be applied to August Föppl and Ludwig Prandtl, theformer would come under the heading "classical type" and the latter under "romanticist".
August Föppl owes his success to disciplined and tenacious work. In contrast, successlands of its own accord in Prandtl's lap with apparently no need for any effort on his part.
At the age of 23, he opens up with his doctoral dissertation a new area in the theory ofelasticity, and at 29, he initiates a new era in hydrodynamics through his work on
boundary layers. Truly, it is a romantic climb! But August Föppl is the superior teacher.
His lectures and scientific works are presentations as clear as a crystal. Prandtl, as ateacher, could not demonstrate that much success. While his teaching was verystimulating for advanced level and doctoral students, he had difficulties with lectures forbeginners. It might have been so because, in his student days, fundamentals of mechanics
posed no difficulties whatsoever for him. They were more or less obvious for him.
Therefore, he could not imagine the difficulties students faced and had to overcome.
With all the respect the two eminent men felt for each other, there were strong
differences, so that occasionally, when they were together for weeks in Ammerland, there
was a little strain in the relationship between father-in-law and son-in-law, although it
never reached the breaking point. The difference in age between the two was only 21
years, but these were times of drastic breaking away from the past, dividing two epochs.
My father still had his roots in the second half of the 19th century, marked by its
authoritarian and rigid outlooks, whereas Prandtl was coined more by social ideas andprogressive thoughts of our (20th) century. Therefore, he found it difficult to subordinate
himself in all respects to our father, as we children did, regarding it as something mostnatural. The powerful personality of August Föppl also exercised a high degree of moral
influence on the people around him so that his colleagues called him ''Gewissen derFakultät'' ("Conscience of the Faculty"). From the bottom of his heart, August Föppl wasvery happy about the big successes of his son-in-law in science. Possibly he was the firstto recognize the genius in Prandtl.
On the basis of my own experience in life, I have gained the impression that a talented
person involuntarily experiences a certain pressure to shape his life in accordance withhis talent. He will feel happy only if he has the opportunity to use his talent. As long as
such an opportunity is denied to him, he will inevitably look for an opening that provides
an outlet to his talent. If he is fortunate to find the proper sphere for activity, he feels
destined to unfold his talent and looks for furtherance to reach the highest possible level.
Prandtl took up only such problems that belonged to the regime of his exceptional talent.
Although he was interested in a broad range of natural phenomena, he restricted himself
to research problems of a special kind, and so, was thrifty in employing his intellectual
potential. By this way, he threw open the doors leading to new areas in research, which
has earned him ever-lasting reputation."52

5. 1911-1918, daily routine
During the early years after marriage that took shape with harmony reigning, there weremany new tasks facing Prandtl. The model laboratory, which was thought of from thevery start as only a provisional facility, did not suffice for purposes of the steadily
growing aviation research. In 1911, again at the suggestion of Felix Klein, Prandtl started
drawing up a plan for a new larger research institute. Geheimrat F. Klein and Geheimrat
von Böttinger favoured the idea of the new institute being built as a Kaiser-WilhelmInstitut. The Kaiser-Wilhelm-Society was however of the opinion that the state of Prussia
should bear a substantial part of the building and maintenance costs. Actual
implementation of the plans drawn up for the institute however dragged on until 1925.
But a first building stage could be finished already in 1918. When the first world-war
broke out in 1914 the project was shelved for the time being. On the other hand, theplanning work for a state-supported laboratory (Reichsversuchsanstalt ) for aeronautics
was pursued with vigour, in which Prandtl, with H. Hergesell, was involved as aconsultant. The laboratory was established in Adlershof in the year 1912 under the name''Deutsche Versuchsanstalt für Luftfahrt e. V.'' (DVL).
An entirely new undertaking for testing of aircraft propellers was started in 1912 in
Arenshausen outside Göttingen. The measurement data were made available to aircraft
manufacturing companies. Prandtl had to cope up with the burden of additional work due
to the large number of requests for advice on technical problems and the expert's reportsthat are a part of the same. The concept of employing the measuring devices to examine
the force exerted by wind was so novel and convincing that one started thinking ofwidening the scope of applications of this method. For instance, bridge builders wereinterested in checking the force exerted on the bridge pillar supports by wind gusts, andthis question was answered satisfactorily by the measurements. Again and again,
inventors approached Prandtl with requests for expert opinion on their projects. I
remember that one in fact believed to have invented a device for perpetual motion. Again
as an example, an unknown inventor sought Prandtl's opinion on his (the inventor's)
work.
Prandtl's reply in 1909:"To answer your question, please permit me to say that, in my opinion, forces due towind cannot be measured at all by the device suggested in the enclosure to your letter..."Prandtl suggested an improvement that he supported by a scientific foundation adding
sketches to the same. When this correspondence came to an end, a solution to the
problem was discernible. Although he was not happy on being approached by suchinventors, he conscientiously replied to every inquiry. I wish to include some further
examples of such correspondence with inventors.
5 December 1912:"Dear Herr K.

53

I have thought about your project carefully and thoroughly and believe it deserves to befabricated. But I cannot conceal that unusual difficulties will still have to be overcome."
22 March 1912:"Dear Herr M.
In reply to your inquiry I am sorry to say that we cannot issue a general expert's
certificate on aeronautical inventions. However, a customer's order can be placed byfiling in an application to the laboratory. The laboratory will then undertake to measure
the forces exerted by airflow on models in experiments. The costs will be invoiced to thecustomer placing the order. They amount to 60 Marks per day of experiment."
9 June 1912:"Dear Herr A.
Your letter of request to Geheimrat Böttinger was passed on to me by him. After taking
note of your descriptions I can only advise you not to follow your idea of a fan flier(Gebläseflieger) any further since that is sure to fail."
The following letter written in 1911 is about Prandtl's desire to help the aviation pioneer
August Euler carry out an air-show in the surroundings of Göttingen. Euler was the first
German to pass a flying test, so had obtained a pilot's license bearing the number 1. Heorganized the first regular air-mail postal service. Later, he laid the foundations forGerman air-traffic laws. The purpose of Prandtl's letter to Senator Friedrich Jenner was toprepare ground for the air-show.
"...Euler wishes to fly over the Kleine Hagen. He thinks it is sufficient to cordon off byteams and security personnel, even if the number employed for this purpose is small. He
thinks the danger lies only if the public, which has paid, feels it is only tolerated so be itmuch more peaceful. Short notices of explanation in the newspapers on the necessity forthe airfield to be kept clear would be, in his experience, very effective. ('No flights takeplace as long as the airfield is not clear.') Euler very much likes all the people of
Göttingen to see something of his flights. It is only access to the aircraft and the take-offsite that he would like to see reserved for the privileged. The costs incurred for the airshow, which consists of transport and travel allowances, costs for material and so on, will
be borne by Euler; Göttingen will be required to bear costs only for erecting barriers andtents for the flying and supporting personnel (a few in number). In the matter ofmobilizing funds there is perhaps a possibility of the city of Göttingen contributing somemoney since the show is for the whole population. The Luftschifferverein (airshipsociety) will also contribute their share and, in return, earn the right for their members toenter the take-off site by showing their membership card. All in all, if the weather is also
good, the air-show may be expected to be delightful for Göttingen.
With best wishes, sincerely yours, L. Prandtl."

54

After the above correspondence by letter, Prandtl had established contacts with August
Euler as early as 1909 at the First International Airship Exhibition (ILA) in Frankfurt am
Main. As a result of these Euler had offered in the spring of 1911 to organise air shows in
Göttingen to promote scientific interest in flying. Prandtl took this opportunity to invite
the then representatives of aeronautical sciences for a meeting in Göttingen. Thus, anaeronautical congress was held in November 1911 at which a number of interesting
technical lectures were presented [37]. Eleven years later, Prandtl recapitulated [41]:"The Congress went on in high spirits in a way I had not experienced hitherto, not in theleast due to the successful part played by the social programme. It did so not in the least
since there was complete agreement regarding the goal to be pursued among all who had
gathered. It is therefore no surprise that the general spirit, also expressed in the speeches,favored the holding of such a meeting again soon. We of the Göttingen society were
given a mandate to organize such a meeting." Von Böttinger, Klein and Prandtl had taken
this upon themselves, and had made preparations for the founding of the society"Wissenschaftliche Gesellschaft für Luftfahrt" with the prince, Heinrich von Preussen, as
honorary president. This society continues to exist today under the name "Deutsche
Gesellschaft für Luft- und Raumfahrt e.V.".
There were also letters with contents of a more private nature in which requests weremade for advice and material help. I wish to give excerpts from these in order tocharacterise his deeply rooted and true humanitarianism.
A rather lengthy correspondence with a person Z. in Göttingen who, evidently, lived in
the neighborhood, indicates the desperate state he was in. He requests Prandtl for a loanof a larger sum of money since he had landed in distress due to speculative trading.
Prandtl is willing to help, and also mediates between the members of the family whowere at odds with each other.
Prandtl, 1 September 1910:
I am very sorry to know of your bad luck through your letters. You have not erred inlooking for help from your former room mate (neighbor). I will give you the loan you
wished for.
Z. answered:"Dear Professor Prandtl,
Thank you very much for your kindness with which you have helped and pulled me outof misery. Your readiness to help is a strong evidence of your friendship, and it has doneme good twofold, since my personal friends---or better said, so-called friends---all left mein the lurch.
Your devoted Z."

55

The conflict between the members of the family could also be brought to a peaceful end
later.
This was Prandtl's way: When requested for advice and help, he was always
spontaneously ready to help. I know of several instances in later days when people
approached him with requests and they got loans from him.
A letter belonging to a different sphere also appears to me to be of interest. In a letter of1913, Prandtl conveys his assent to his membership of Keplerbund. The society
Keplerbund for furtherance of knowledge on nature had framed a set of scientificrequirements and principles which were as follows.
1. Freedom of science,
2. Objectivity in research,
3. Support of science and natural philosophy,
4. Acceptance of inadequacy of science to define a Weltanschauung all by itself,
5. Acceptance of neutrality of science in questions of Weltanschuung and religion,
6. Hold the opinion of the right to believe in God, i.e. its compatibility with scientificthought, as a logical consequence of point no. 5.
In his letter of agreement for membership Prandtl wrote as follows:
25 March 1913:"It is only now, after close of the semester, that I am replying to your circular sent quite
some time ago. I have given a genuinely sympathetic thought to the matter in your letterand find I can subscribe to all the six points you list therein. I am also in complete
agreement with the objectives of your society, if, in putting them into practice, the''guidelines'' as laid out are followed. Opinions expressed earlier, which were obviously
coming from unfavorably disposed quarters, had given me the impression that the goalof the Keplerbund is to lead those interested in sciences to the old positive religions.
I suppose I can presume from the guiding principles set out in your circular that the
Keplerbund, just as it works against subordinating the religious outlook to realization of
the truth of nature, also stands against interference by ideas traceable to religion in
unprejudiced pursuit of the sciences (belief in supernatural powers etc). If thisinterpretation (of mine) of your objectives is correct, I will be glad to be a member ofyour Bund.
I wish to mention one point of inaccuracy in your circular that drew my attention: there istalk of an ''artificial animosity'' between sciences and religion, for which monisticmaterial circles are held responsible. In my opinion, the positive religions that havestemmed against scientific research, in particular against the theory of evolution, aremore to blame for this animosity, and monism is only a reaction to this backward
leanings, although an overreaction shooting far beyond the goal. "56

The load of work increased many-fold in these years, as already mentioned. Prandtl saw
the necessity to look for an assistant for his undertaking. In response to an advertisement
for the post of an Assistent in the Modellversuchsanstalt (Laboratory for Model Testing),
there was an application from only one young scientist who had worked in the field ofhydrodynamics. As Prandtl showed him around the laboratory, they talked with eachother with excitement. Obviously this young engineer was highly talented and excellently
suited for the post. It was Diplomingenieur Albert Betz, who was to become later
Director of AVA, who was appointed as a "Hilfsassistent" to Prandtl on 1 September
1911. There were, however, only a few years of research work together possible, until
war broke out. Albert Betz then reported himself voluntarily to do army service. But
within the following year, it turned out that he was indispensable in the Institut. Prandtl
therefore wrote to the "Kurator" on 25 June 1915: I would request your Honor to makethe arrangements necessary for Dipl. Ing. Albert Betz, who was a Hilsassistent earlier, tobe employed again in his earlier post, for the work of assisting the building up the
Modellversuchsanstalt. Dipl. Ing. Betz was doing voluntary war service in the army, but,was discharged from the army and placed for services at my disposal."
And it happened that way too. After his final discharge from war service, he was back in
his earlier place of work.
Most of the assistants and technicians of the Institut were drafted to army service sinceAugust 1914, so in the beginning, Prandtl had to run his undertaking without the trained
personnel.
In 1912, the Motorluftschiff-Studiengesellschaft (Society for Study of Powered Airships)
was dissolved, and thereafter the Modellversuchsanstalt was taken over by the university
and annexed to the Institut für angewandte Mechanik (Institute for Applied Mechanics).
The running expenses were borne by the Ministry of Education (Kultusministerium). The
success of the laboratory was all too evident, and the facilities that were developed first
here served as an example for other research centers of this branch of science. But, as
said earlier, the first world-war brought the planning work for a larger laboratory to a
standstill. However, in 1915, the army's directorate declared its interest in further
development of the Modellversuchsanstalt. The army and the navy had made continuous
use of the experimental facilities that hardly met the requirements. So, Prandtl wrote a
new memorandum (Denkschrift) to emphasise the necessity for building a new facility. I
will quote from this memorandum:"The trend of development taken by the work done at the Modellversuchsanstalt hasgiven rise to the thought that it would be in the interests of the army and navy
administrations to help establish a larger aerodynamics laboratory that is suitable for
dealing with foreseeable problems in the development of military and naval aeronautics
by granting funds for starting the laboratory and to cover its recurring expenditure."
The memorandum was handed over in person to Prince Heinrich of Prussia in Kiel, who
forwarded Prandtl's plan with a personal recommendation to the War Ministry and to theReich's Admiralty:

57

"Kiel 30 April 1915
Respected Professor Prandtl,
On the occasion of my visit on the 27th of this month to the ship-yard Max Oertz,
Hamburg, which was to inform myself of the progress being made on the presently very
important task of building sea-borne and land-borne aircraft, Herr Oertz handed over tome your memorandum that had been received the same day together with three copies of
an off-print from the Zeitschrift des Vereines deutscher Ingenieure (Fachgebiet
Luftschiffahrt)---(Journal of the German Society of Engineers (Aviation Section)). Whilehanding over these documents, he added the remark that it is important that they reach theproper authorities, and requested me for assistance in this matter.
Being convinced of the importance of the contents of the documents and of the necessity
to enlarge and support the Göttingen undertaking, I offered to do the needful witheverything within my means, and have already sent two copies each to the War Ministerand to Admiral Dick of the RMA (Reich's Admiralty) with a covering letter. In the
covering letter, I have attempted to state briefly the mutual connection that exists between
the Göttingen institute and airplane builders, pointing out that the stage of empiricalstudies has in fact been crossed and that science, besides primarily supporting building ofaircraft, furthers the cause by scientific investigations and establishment of facts.
Although I am not in a position to judge or influence official thinking in financial
matters, I am happy that I have been able to draw attention to a matter which, for one, isvery dear to me, and, to the close relationship between science and design that was also
proven beyond doubt by Herr Oertz's lecture supported by design drawings. A goal that I
have always dreamt of has been reached with this, and will probably be further pursued.
This is primarily thanks to your efforts. The nature of events in the years 1914/15, and in particular in the past 9 months, havebeen such that I have not been able to attend personally to these details, but I am happy
there has been an opportunity for me now.
The sole purpose of these lines is to let you know of this.
In the hope of succeeding to extend due support to you in your efforts in favor of theReich, I send you my hearty greetings and remain, my respected Herr Professor, yours . . .
Heinrich Prince of Prussia"
Shortly thereafter, a meeting took place in Berlin of which Prandtl soon sent a note of
information to Felix Klein. His shock over the losses and suffering in the war are veryclear.
Berlin, 11 May 1915:

58

"Dear Herr Geheimrat:
The outcome of today's conference in the War Ministry is simply overwhelming, in order
not to say devastating (particularly from the standpoint of my existence). The decision
has been taken to release war funds for the new laboratory for model experiments which
will be built as fast as possible on the Böttinger lawns in order that the measurement data
may assist war efforts." (Geheimrat Böttinger, Commercial Director of the company
Bayersche Farbenfabriken in Elberfeld (now a district of the city of Wuppertal), had
placed his plot, bought in 1907, at the disposal of the planned extension.) "I havepromised the first results in half a year, which was declared as acceptable. According tothis, the officials reckon with a prolonged period of war. I have already reclaimed myAssistents, will restrict my teaching activities, perhaps will have to give up the dean's
position. Everything else in person.
Prandtl"
Just like Albert Betz, the other young Mitarbeiter, Dr.-Ing. C. Wieselsberger, could also
be brought back from army service. G. Fuhrmann had already fallen in the war in
September 1914 in Belgium. Betz and Wieselsberger were employed as Hilfsassistent on
15 May and 1 June 1915 respectively. The engineer Dipl.-Ing. Max Munk had alreadyobtained the post of a Hilfsassistent in April. Thus, making progress was assured in
executing the plans for extending the laboratory. In July 1915, the brother-in-law, Dr.
Hans Thoma, was brought in to lead the building works in the new project in Göttingen.
In the meantime, Else Föppl, Gertrud's sister, had married Hans Thoma, also a talented
engineer. The co-operation at work with Thoma, whom the Imperial Docks (Kaiserliches
Werft) in Wilhelmshaven had released up to 1 March 1916, enabled good progress to bemade at putting up the new extension buildings.
On 29 May Ludwig Föppl wrote in a field post letter "Wireless Command no. 6: I learned
from Gertrud that you are getting a new Institut now, upon which I wish to congratulate
you. How much would your colleagues all envy you for serving your mother country(Vaterland) this way. I also congratulate you upon getting a person of ability like Hans
Thoma as an Assistent."
23 June 1915:"You are now actively working in the service of the mother country bypushing ahead putting up the new buildings of the Modellversuchsanstalt. We, thewireless people, can establish without doubt that the enemies are superior to us in flying."
In the course of a few months that were full of work, a new high performance windtunnel with a settling chamber of 4 meters × 4 meters and a jet diameter of 2.25 meters
was built, opening new avenues for research.
Professor Betz writes [3]: "Although during the war military interests were, naturally,
given the topmost priority, it was noteworthy that the offices responsible gave thelaboratory wide freedom to choose the tasks they set for themselves. There was a general59

conviction regarding the importance of basic research on a large scale, and it wasconsidered most promising if the researcher was helped to implement his ideas without
forcing him into a straight jacket at work."
It is against the background of this concept of freedom of research that an inquiry by abiologist regarding animal flight can be understood. Here is Prandtl's reply:
20 August 1915:"Dear Herr Doktor,
Unfortunately, the conditions prevailing do not permit me to say things favorable. The
Laboratory for Model Testing that is being built now is financed out of war funds, andserves only flight technology. The laboratory gets a bigger and more powerful air-stream
in which airplanes and parts of the same can be tested for their drag in flight. Other
facilities are not foreseen at present, and will be added only if military interest is evident.
But it is planned to continue building up this institute in peacetimes too. The question ofwhether sometime later special studies could be devoted to biological aerodynamics isstill far away. You know that my attitude towards such questions is a sympathetic one,
although I am more and more convinced that airplane technology has little to gain fromstudies of animal flight. In my opinion, conclusions useful for airplane technology are
more likely to be drawn from flight studies of big birds (stork, condor, big marine birds).
Smaller birds and more than even these, insects, fly under conditions so different fromhuman flight that their study is hardly likely to further airplane technology. Of course I
am not disputing in the least that research in these areas is fascinating and educative froma scientific viewpoint. After having said this, you would understand that, at present, I
cannot give any assurance of biology of flight being accorded greater importance in theInstitut. However, I believe to be able to say that, when the Institut sails in calmer waters,
it will be possible to procure apparatus and facilities for conducting such experiments."
The job awaiting the Modellversuchsanstalt in its new building was to deliver the resultsof measurements to the army directorate. An able mechanic was urgently needed for thispurpose.
Prandtl wrote to the Reich's Admirality on 8 December 1915:"The orders placed by the Imperial yards with the Göttingen laboratory have resulted inpiling up of work in such huge proportions that, with the strength of personnel presently
available, this work can be done only with much delay. I am therefore taking the libertyof asking the Reich's admiralty if it would be possible to place the services of a helper
assistant (Hilfskraft) at my disposal for this work. One suited for this post would have thequalifications of a technician who is capable of taking readings from measuring
instruments following instructions given to him, reduce the data and draw the curves forgraphic evaluation work."

60

Since his suggestion was rejected, Prandtl wrote to the deputy of the general command in
Magdeburg to get the release of the mechanic Julius Lotze who had worked with himearlier, released.
On 15 February 1916 he wrote:"A laboratory for model experiments for aviation is presently being built in Göttingen
under my guidance out of funds provided by the war office. Since it has not been possible
to obtain mechanics for fabricating the measuring instruments for this work in sufficientnumbers out of personnel freed from army service, I wrote sometime ago to Grusonwerke
in Magdeburg-Buckau requesting them to return to my services the mechanic Julius
Lotze who worked with me earlier. Herr Julius Lotze has been sent by orders of the war
ministry to Grusonwerke as a fitter for their cannon workshop around a year ago. Since
Lotze is not just a highly skilled mechanic, but possesses, due to his earlier work, thespecialized knowledge required for the experimental work to be done, his assistance isinvaluable for me in my work mentioned."
Prandtl succeeded in getting back Julius Lotze from Grusonwerke to Göttingen, where he
was of much help in building up the new laboratory.
In the meantime, the need had arisen to employ a new secretary too. Prandtl madeenquiries with his colleagues with the object of finding a suitable secretary. Problems,
even those of employing a person, could be solved most reliably through personal
relations. Professor Wiechert, director of the seismographic institute, had an excellent
typing assistant, one Fräulein Frieda Kreibohm, who also did technical calculation jobs.
Enquiries were made if this lady perhaps had a sister who could be employed. The sister
was only 16 years old then and was still at school. When an offer was made to her to be
employed immediately, she chose not to give up school in the last school-year. Until thenProfessor Wiechert could lend to Prandtl the services of his secretary for half a day. The
work that had to be done was to reduce the measurement data gathered in the course of
the experiments. On the very same day on which the younger sister, Hilde Kreibohm,
passed out of school with the final standard examination, she went in the afternoon to thelaboratory. She stayed there for over 50 years, for her whole working life; rising from thesmall position of a typing assistant to a senior secretary. When I visited here, I only asked
her: "Can you type on a typewriter?" "No," she answered, "there were no courses offeredthose days. Professor Betz arranged for an old typewriter to be brought to our home forme to try out, and I learned practicing for hours."
Personnel strength in the office and the workshop grew steadily as the buildings of theInstitut neared completion. In 1918, the personnel strength reached its record mark of 50
people. Dr. Wieselsberger and Dr. Betz headed a section each, for new design andtheoretical work. There were among the helper assistants (Hilfskräfte) many students
doing voluntary war service, so that the work of doing calculations could be done as
desired. On 7 March 1917, an air stream could be generated for the first time. Prandtl
made a note of this date himself.

61

Since the distances to be covered between the old and the new laboratory resulted inmuch loss of time and the old brick barracks had turned unsafe in some respects, it was
moved in 1918 to the new plot of land given by Böttinger. With this, the plans of putting
up buildings reached completion in a certain sense.
When the new building was completed and the military administration was more liberalin placing personnel at the services of the laboratory, it was again possible to conduct,
besides the experiments, theoretical research work. Now Prandtl could once more take up
work on wing theory that he had started in 1910 and bring the same to a stage ofcompletion. The aim of this difficult theory was to explain how the relationship between
lift and drag is influenced by the shape of the wing. At the meeting of the Gesellschaft
der Wissenschaften zu Göttingen (Göttingen Society of Sciences) on 26 July 1918, he
was heard presenting wing theory for the first time [33].
In his article felicitating Prandtl on the occasion of his 50th birthday Th. v. Karman wrote
on the significance of wing theory [16]: "The main contribution of Prandtl to airplane
technology is without any doubt his wing theory; more precisely, the discovery andevaluation of the so called 'induced drag', which paved the way for rational design
calculations of airplanes, and in particular for calculation the influence of the span, forcomparison of monoplanes (Eindecker) and biplanes (Mehrdecker), and of the influenceof limit and stagger, all at one stroke. The analogy between a wing and a line vortex wasprobably known. Even the fact that, for a wing of finite span, the circulation at the tips if
the wing cannot just disappear, but a 'braid of vortices' has to separate out, wasestablished by Lanchester. The genius in Prandtl saw, however, at a glance that
Helmholtz's theory of vortices, consequently applied under assumptions of lightly loaded
wings, should lead to a complete theory for idealized wings; a theory that yields
information on lift distribution, power requirement and so on that are independent of the
profile drag. The discovery of (the existence of) minimal drag of the ideal wing, the socalled 'induced drag' is as significant for airplane construction as the discovery of the'Carnot process' for the design of thermodynamic machines. Both deliver a reference
scale for measuring the quality of the design, which is a basic principle according towhich the huge volume of information contained in experience up to the present day
suddenly became transparent and understandable…"

62

6. A day at home
In spring 1914 my parents had moved to a more sun-lit and modern apartment with bathand central heating on Bergstrasse (now Calsowstrasse). The main reason for the move
was that offspring was expected. In November 1914, the happy parents could announce
the birth of their first daughter Hildegard. A second daughter Johanna was born two andone half years later. Now the big apartment was full of life. At that time, the house wason the outskirts of the town; adjacent to it were beginnings of a plum avenue and several
trails that led to meadows and allotment gardens. There was no garden of our own, but
the meadows and woods in the neighborhood were splendid playgrounds for us children.
My sister and I grew up there in much freedom. My mother, whose father was a strict
disciplinarian, did not want to bring up her children sternly. She knew to guide us withlove and understanding, but was firm in not allowing us to get away with any mischief.
Understandably, she had taken over upon herself the main responsibility for bringing us
up since our father whose thoughts were fully occupied with his plans, gladly left thistask to his wife. When we children sometimes impetuously demanded of him to play withus, just when he came home tired, he could hardly resist our assaults. But my motherinterfered at the right time saying: "Leave your father in peace! He wants to rest a little
now!" By the way I clearly remember that she sometimes said: "You do not know what agood father you have."
Shortage was ruling everywhere during the post-war years. Even the coal ration sufficed
for heating of only one oven. When Father was at home, which was seldom, for instanceon a Sunday, we were admonished to be silent in order to keep disturbance to him as low
as possible. I remember a scene that took place in the living room of the family. My
mother was firing the oven, kneeling on the ground and poking in the embers. When she
was thus engaged my sister and I did some mischief that angered her. Father was sittingat the large table, bent over his work. Mother's words of warning and rebuke went
unheard, and the mischief was in full swing. She then turned to her husband appealing for
support since, with her hands dirtied by coal, she couldn't inflict the punishment herself:"Ludwig, please give the children a beating." Father pushed his papers a little aside, got
up and walked towards our play-corner. We were very tense waiting for the unusual
punishment to be meted out by our father. The tension just couldn't get any worse. He
hesitated a little when he stood next to us, turned to Mother and asked her to "clarify"
what he was supposed to do: "Yes, but where?" We two sisters burst into laughter ofrelief---even our mother could not arrest her laughing. Even now I can clearly remember
how Father tried to explain to us that his query was justified, since the measure ofpunishment had still to be decided, depending upon the offence that he had not observed
himself. He would not have come upon the idea on his own to inflict physical punishment
upon us- no, this thought would be absurd. Thus we often came away from suchpunishment when he was around, although we caused much disturbance to him. Later, hetook over the particular responsibility at bringing us up through his loving words, which
made us see the point and taught us proper behavior.
The serenity of his nature could be felt when he sat at the table and worked, totallyabsorbed by his immediate surroundings during writing and doing calculations. His

63

caring wife knew mostly how to keep us away. She encouraged us to jump aroundoutdoors; and, as already said, Father was mostly in the Institute, and we were permitted
to bring home our friends for playing.
Shortage in the post-war years, particularly in supply of food, had caused a state ofgeneral misery to set in. Prandtl wrote about this to a Swedish colleague, Professor Oseen
in Upsala, with whom he was regularly in correspondence for years: "It looks very bad in
the poor German mother-country, and it will get worse. One half of the German
population should really be in the sanatorium in order to heal the effects of undernourishment. Here in our place, food is in short supply, but, the countryside being in theimmediate neighborhood, matters are not as bad as in the bigger cities. When necessary,
one can just walk to the villages where there is still something."
My mother went mostly twice a week walking through the woods to the family
Christmann in Herberhausen whom she knew well, and from whom she got milk for her
children, and in fact often some butter and a few fresh eggs. Over the week-ends, ourfather also had the time to accompany her to Herberhausen. All of us then sat in theoverheated living room, the grown-ups talked with each other, and we children tookpleasure in looking around in the court and the stables. Our parents knew every trail in
Hainberg well, and sometimes we returned home when it was dark. Thus, the week-end
trips were full of adventure for us. People living in the smaller cities with no public
transportation had to be able to cover much larger distances on foot than today.
Even during the week it was a regular habit for Prandtl to walk to his place of work.
Prandtl was seen on this daily route lost in thought, looking inwards, hardly noticing
passers by. But he took note of many small things along this route. In spring he looked
for the first flower blossoms to come up behind the hedges of the small front gardens, andwas joyous to see the snowdrops, and later violets and roses. He knew the planting
patterns of these gardens very well, and followed their flowering time year after year.
When we were all together at the table for lunch or dinner he made it a point without failto mention his observations. On the way home, he was often accompanied by his younger
Mitarbeiter (co-worker) who welcomed this opportunity to discus their scientificproblems with Prandtl. The discussion usually went on for a while in front of our housealthough lunch hour had passed. A young physicist is supposed to have pronounced thefollowing dictum: "If one is too lethargic to think over a problem cropping up, one justhas to tell Prandtl about the same. Either he can clarify it straightaway since he hasthought over the same problem long ago, or, being stimulated by the question, he will not
be in peace, and he will tell you the solution in the course of a few days." 1)1) Taken from a talk given by A.Betz "Das Lebenswerk von L. Prandtl"[4].

647. Gliding
There was no stagnation in the special research work during the post-war years althoughsevere restrictions on powered flight were imposed upon Germany by the treaty of
Versailles. Dismantling in some works also hit aviation hard. On the occasion of ameeting of the Wissenschaftliche Gesellschaft für Luftfahrt (Scientific Society for
Aeronautics) in Augsburg, a visit was arranged to the Riedinger balloon factory which
was mentioned earlier. A newspaper journalist wrote:"On entering the large hall a cloudof sadness descends upon a lover of the mother country, since it contains remains ofaviation equipment that succumbed to the rage of destruction even here. It went to theextent that even the baskets of the fetter balloons (Fesselballon) had to be cut into
pieces."Insofar as flying was concerned, there were sources of new impetus coming fromstudents enthusiastic of flying who now devoted themselves to gliding. This was not in
violation of the treaty of Versailles. Flying enthusiasts formed themselves into groups atdifferent universities, and these fabricated their gliders themselves. Flying as a sport
activity did not have military goals and hence could be pursued freely without being
troubled by vigilance from the winning powers. The editor of the aviation journal of
those days Flugsport, Oskar Ursinus, got the idea of calling for a gliding competition.
The young designers were supposed to bring their gliders and assemble for thiscompetition upon the heights of the river Rhön. Many types of gliders were brought overthere and their pilots wanted to enter into the competition. The Rhön terrain was chosen
for this purpose since there was a steady wind blowing over the treeless knolls there
which could be used both as updraft and fair wind. The participants in the firstcompetition in 1920 could fly for about only two minutes. The individual flights weretimed accurately. In the second Rhön competition that was held in 1921, the winner W.
Klemperer succeeded in flying for a duration of as long as 13 minutes and therewith set
up a world record. As part of the efforts put in to improve this performance manyrefinements to the equipment were undertaken, and there was a willingness to learn moreof the theory of flight. Seminars were arranged in response to this and were held on thewater knolls (Wasserkuppen) there to instruct the young glider designers inaerodynamics. Prandtl and von Karman, Runge and Madelung taught them that correct
and functional design was what mattered most, and also how to use to advantage the air
stream under favourable weather conditions [21, 29]. In 1922, as a Berlin newspaper
article reports, the record in flight duration already reached three hours. The number ofparticipants in the Rhön competition increased, and so did the enthusiasm for this new
sport activity. The hand-made models, each designed individually, also meant personalcommitment of the one concerned. Excellent team spirit prevailed in the group. There, on
the top of the water knolls, modest barracks had been built where the flying sportsmen
stayed partly even over winter, using every favorable day for practicing. The Rhön
gliding competition was in existence for many years [48]. On 25 July 1926, Prandtl got
the following letter from the organizers of the competition:"Respected Herr Professor,

65

We have the honor to send you herewith a list of the gliders registered for thecompetition, and a permanent pass with a badge as a member of our distinguishedpanel/committee (Ehrenausschuss), and hope to welcome you on the water knolls."
During this period our family was on a Pentecost (Pfingsten) trip in the Rhön area. The
narrow gauge train took us from Fulda to Gersfeld. From there we began climbing up to
the top of the knolls. It was warm and sunny at the lower altitude below, but at the top it
was very windy and the sky started getting clouded. When we reached the top a flying
sportsman was getting ready to take off. The glider had to be towed for a short distancewith a tug by his fellow-sportsmen, and then it had to gain altitude of its own. Our father
watched the flying sportsman spellbound and with deep satisfaction at the same time until
he disappeared from our eyesight. After lunch, which we had in the main building, ourfather was fetched, since the gliding sportsman who had landed in the meantime, wanted
to talk with the fluid flow professor over his flight and consult him on some problems
that had arisen during the flight. In the afternoon it started raining, the knoll was soon
clouded in fog, and the flying was called off.

66

8. The 'Call' to Munich
In the summer of 1920 Prandtl got a 'call' from the Munich Technical University(Technische Hochschule München). His father-in-law, August Föppl, had sought them torelieve him of his duties on his reaching 66. August Föppl still kept some smaller tasks in
the laboratory for himself, but he wanted to withdraw from his lecture duties inmechanics attended by more than 400 students. At the time of refilling the post it wasplanned to divide the overburdened Lehrstuhl (chair) into two, so that the conditions ofwork looked quite favorable. It is easy to imagine that the prospect of returning to theirhome region of South Germany was very attractive to my parents. But Prandtl purposely
postponed for some time taking the final decision, since that was not easy for him.
I would like to quote a few passages from a letter written by Prandtl in this period to Herr
Geheimrat Dr. Duisberg, Director-General of the company Farbenwerke Bayer. Prandtl
had been given hopes of being granted financial support for his steadily increasing
research plans channeled through the newly founded Helmholtz-Gesellschaft (Helmholtz
Society). That would have kept him in Göttingen.
20 November 1920
"With reference to the 'call' I have received, you were kind enough during our meeting in(Bad) Nauheim to indicate the possibility of extending financial support for my research
institute in an effort to persuade me to stay in Göttingen, so I am taking the liberty ofwriting to you in this matter which is still awaiting a decision:
What makes the Göttingen position valuable to me is the research activity. Against thisthe teaching is not of much significance due to the small circle of interested people thatmy area of research finds at the university. Probably, I have to shelve for ever researchplans as envisaged before the war for the KWI (Kaiser Wilhelm Institut) for
Aerodynamics. I will have to be content with conducting the research work on a muchsmaller scale. But even for this, substantial amounts will be necessary to meet recurring
expenditure."
It is not known to me how the matter in respect of financial support was supposed to besettled. In the meantime, news reached Prandtl that due austerity measures, the Lehrstuhl
could not be divided into two. Prandtl was not willing to accept the extra burden
associated with such a large number of students. He would then have had hardly any timeto spare for his research work. In August 1921 he therefore rejected the 'call' from
Munich. He then made recommendations to the committee as to who could be anothersuitable candidate.
Exactly one year later the offer from Munich was renewed, since, in the meantime,skillfully conducted negotiations had cleared the way to split up the Mechanik-Lehrstuhl
into two. They were to handle distinct fields in the very broad area of mechanics and each
was instituted with a chair for this purpose. One of these chairs had already been given to
Ludwig Föppl. This time Prandtl decided in favor of Munich. On 30 December 1922 he67

gave his assent. The actual move was delayed since searches for housing accommodationin Munich were in vain. This was in the middle of the inflation period, and the rent for anapartment was, as were the prices for all "goods", steadily escalating. In this phase ofhighly tensioned planning (some terms were still under negotiation: the position of an
Assistent and an exclusive budget for the laboratory were to be applied for) Prandtl
unexpectedly received an offer from KWG (Kaiser-Wilhelm-Gesellschaft). The promise
was given to him that, in case he decided to stay in Göttingen, a new Institute for
Hydrodynamics would be built for him next to the buildings of the AVA that existed
already. Everything got turned over once again and Prandtl decided to stay. But there wasa set-back again, since due to the disgrace of the finance minister the money approved by
KWG could not be disbursed. My parents were occupied with plans for the move again. I
still remember a little of the hither and thither that was going on. A small incident
clarified to me the meaning of what destiny had in store for us personally. Once, when we
had plucked marguerite (Oxford Illustrated: ox-eye daisy) flowers on the lawn in theneighborhood with our mother, and we sat on a bench on the border of the woods, shepicked up a flower from the bunch, and pulled out the white petals one by one to ask
destiny playfully: Munich-Göttingen, Munich-Göttingen and so on. I cannot say any
longer which of the two the marguerite oracle prophesized then. Only, I became very
conscious of how heavily the yet to be taken decision was burdening my parents' state ofmind.
There are letters left from the last phase of this development that Prandtl wrote to Ludwig
Föppl to keep him informed of the then current status in this matter. They go to show
how much he struggled to come to a decision that would be fair and just to all concerned.
Prandtl to his brother-in-law Ludwig Föppl:13 July 1922:
Schröter asked me, of late, if I was prepared to accept the 'call' from Munich. I explained
to him that I am strongly inclined to accept, but that I could not give a firm commitment
before negotiating terms with the ministry.
On one matter I wish to sound you for your opinion. During the immediate past, due tothe deanship I have not been able to work out my research ideas. There is no dearth ofideas since my doctoral candidates, whose numbers run into quite a few (almost half adozen), keep me on my toes to think over matters for them. My strong desire is therefore
not to have to sever all this, and I do not wish to leave the doctoral candidates entirely totheir fate. Hence it is very important for me to be able to stay here until next Easter."
17 January 1923 to the brother-in-law:"You would have come to know through letters to the family that I have accepted theMunich offer now, but have not yet given the date of joining, which has to wait until I
find an apartment."

68

27 April 1923 to the brother-in-law:
In the light of the thinking going on regarding what I will be offered here, I of course
wish to be certain that, if I go to Munich, there will be good openings there for me forresearch in hydrodynamics."
2 June 1923 to the brother-in-law:"I am sorry to inform you today that the matter of the "new offer from Göttingen" hasreached a critical stage. The intention that is made known--- and it seems to be almost
certain that it comes through--- is that within a very short period, on the basis of April
this year, a sum of 40 million per annum and a one time 500 million, would be mobilized
to be offered to me for building the hydrodynamics division in the scientific departmentof the research institute proposed to be built. I am enclosing a copy of the letter I havewritten to the executive managing director (Geschäftsführer) of the Kaiser-WilhelmGesellschaft in reply to his letter in which he requests me to respond by return of post if I
would stay here when the intentions are confirmed:“2 June 1923 to Dr. Glüm, Director:
Unfortunately it is not yet possible for me to comply with your wish to inform you of myultimate answer today itself should the ministry give their definite approval to the sumsof money offered. It would not be right to take a decision on a matter that drasticallyaffects my personal future without at least a few days of thought.
As I conveyed to the Curator of the University yesterday when he called me in, I do
recognize the stupendous accomplishment in obtaining such large sums in these times
from the Reich and Prussia. The commitment to this cause by the Kaiser-WilhelmGesellschaft and the Prussian ministry of education, that finds expression in reaching thisgoal in such a short time, compels me of course to give the matter a serious
consideration."
13 July 1923 to the brother-in-law:"As you would see from the enclosed copies of my letters bearing the same date to theministry and the rector's office, after much thought in the matter of my 'call' to Munich, I
have now decided, to make the decision in favor of Göttingen. While doing so, I cannot
push aside the sentiment of feeling sorry that plans for our working together cannot bematerialized. You have to start afresh to fill in the vacant position, and I wish you successin finding a suitable person. If you get a good teacher who applies himself full of energy
to the work of teaching, you will probably have struck a better bargain at the end of the
day than with me, if I, contrary to my good intentions, cannot shake off the research habit
sufficiently."
13 July 1923 to the Bavarian Education Ministry:69

"I have the honor to inform the Ministry for Education that, in the matter of my 'call' to
the Technical University of Munich, a new situation has arisen through the Prussian
Education Ministry and the Kaiser-Wilhelm-Society for the Advancement of Sciences(Kaiser-Wilhelm-Gesellschaft zur Fördering der Wissenschaften) letting me know of
their intention to offer a sum that is high by to-day's standards for realizing my earlier
plans for a hydrodynamic research institute. According to the information passed on by
Berlin, the sum proposed for approval is 500 million, based on prices prevalent in April."
On 27 June (1923), candidates for filling the vacant professor's position in Munich weresuggested to the brother-in-law. We may give here one suggestion of his:"I know of only one candidate who satisfies all the requirements mentioned earlier, that is
von Karman in Aachen. He has done outstanding work in all fields, some of them haveopened new vistas. Besides, he is, as you know and as I hear again and again, a brilliant
teacher. I am of course entirely aware that, due to his lineage, extending a 'call' to him
might cause difficulties, but in my opinion such principles should not go so far that auniversity consciously destroys its scientific life."
So, already at that time Prandtl, in contrast to his Munich colleagues, pleaded without
prejudice in favor of an esteemed Jewish scientist.
14 July to the brother-in-law Ludwig Föppl:"My voluminous report with building design drawings and cost estimates for theHydrodynamics Institute has gone to Berlin last Thursday. Since the concerned Berlin
authorities are very much interested themselves in the matter making rapid progress, I
believe, one will not have to wait for long for a decision."
24 July to the brother-in-law:"I could resolve to give an ultimatum of 8 days to the Berlin people to the effect that I
will decide in favor of Munich once this period of my ultimatum runs out. Of course anecessary prerequisite is that there is a suitable apartment for us."29 July, Gertrud's letter to her brother:"I often have the feeling that the present time, that is as unedifying as can be possibly
thought of, will not be very favorable for building the new institute. I have tried a lot todissuade my husband from this plan, but I have seen he is very much attached to theidea."
5 August to the brother-in-law:"The Berlin people react with bitterness to my threatening letter and say that everythingis already being accelerated. But the matter is very complex due to many authorities
being involved."

70

7 September to the brother-in-law:"I talked on the water knoll with the official in the Reich's finance ministry who isconcerned with matters of aviation. He confirmed that their intention is to advancebuilding the Annex to the Institute under all circumstances, particularly due to thestrengthening of German aviation interests which one expects to achieve from it. Given
this, it appears to me as if I had no right any longer to tax the patience exercised by all ofyou in Munich."
11 October to the brother-in-law:"I was in Berlin during the last few days for a conference of the Wissenschaftliche
Gesellschaft für Luftfahrt (German Aeronautical Society), and took the opportunity totalk with the Kaiser-Wilhelm-Gesellschaft (Kaiser-Wilhelm-Society). There they werevery unhappy over the last crisis of the Government, since they had just succeeded inwinning over the Finance Minister Dr. Hilferding to include my Institute in the budget
just when he had to quit office. If it had not been so, a decision for me, however in asense unfavorable to you, would have been within reach within a very short time. Now ofcourse no one knows what course the matter will take."
29 October 1923 to the brother-in-law:"If you ask me whether I still believe in my Institute being set up, I must of course replythat in the very moment, when things happen in Sachsen and Bavaria is rebellious, it
looks pretty bad. At the end of the day it is not a matter for my private opinion, but one
for those concerned in its cause to whom I have committed myself. But tomorrow I will
push Berlin for a decision. I would rather wait for a "No" from Berlin than throw away
the thing myself since I want to depart on good terms with the Kaiser-WilhemGesellschaft with whom I will still have things to do in the future."
28 November to the brother-in-law:''After the new Cabinet crisis it is almost certain that I will leave Göttingen, so I thought alittle woefully, and had much discussions with Gertrud on how we would set up ourselvesin Munich.
Just then news came in from the Kaiser-Wilhelm-Gesellschaft that there would be a new
opening for the Göttingen institute through a donation from an industrial magnate. It had
the same effect on both Gertrud and myself, we were unhappy to have to give up Munich
again. As a matter of fact we both are attached to Göttingen AND Munich, but only oneof these can be THE reality.
Since I am not in a position to foresee the development, it if left to the Munich people todecide for how long the decision can be postponed."71

28 November 1923 to the Rector of the Technische Hochschule Munich.
"Respected Magnifizenz,
It is extremely embarrassing to me to have to request you to give me a little more time
instead of giving a final answer. I am doing so at the urgent request of both the KaiserWilhelm-Gesellschaft (KWG) and of our present faculty. Due to the Cabinet crisis in
Berlin, an opportunity to get an approval for the planned Institute has again failed
although rudiments for starting were good.
However, the executive director of KWG who has been very entrepreneurial andenergetic in this matter, has not given up for good. Instead, he surprised me by opening
new prospects in which co-operation of a rich industrial magnate is a keystone, andentreated me to give him at least a few days' time. I am very conscious of my having noright to ask the Munich Hochschule to delay any further. But the request from KWG
appeared to be sufficiently well founded for me to pass it on to the Munich Hochschule.
If there is a possibility of establishing the second part of the research institute in
Göttingen, and if this can be accomplished by my staying here, I feel it is my duty to
devote myself to this task and thus carry out mission in life started, which is to continue
research into the laws of motion of air and water. If this opening is closed my energy willlie idle, and I am convinced that in this case I can use it better in Munich."
3 December 1923 to the Rector of TH Munich:''I have the honor to inform Your Magnificence that, according to a piece of news justreceived, building the institute here may be regarded as assured. The agreement reached,
therefore, asks me to refuse the offer of the Professorship for Technical Mechanics in
Munich. Even a few days ago I had expected things would go in exactly the opposite
direction, and find it painful that now nothing will materialize of my plans that I had put
together for work in Munich. The task before me in the immediate future here will be,
due to the times, very difficult, but, if it is carried out in its main parts successfully, it will
give me a bright opportunity for doing work in areas that are very close to my heart.
I request Your Magnificence to inform your Munich colleagues that even now, when mymoving to Munich has been dropped, I feel strongly attached to Munich and will beavailable in every way when they need me.''5 December to the brother-in-law:
You would have come to know from your Rector that the Institute has indeed beenpromised to me and therefore I will stay in Göttingen. I ought to be really happy over the
coming research opportunities, but it has not gone that far up to now. The unhappinessover everything that I had pictured myself for my Munich stay and lost now, is still rulingwith the upper hand. In addition, there is the concern that there may still be an obstruction
coming in the way of building the Institute. But I keep on telling myself that, when others
are offering me an opportunity for extensive research being regarded as the leading72

expert of this area in Germany, I should not pull it down myself. I am quite hopeful ofderiving much satisfaction out of work here when once the coarse work is done.
The children, getting to spend much time outdoors, are well. The Bergstrasse here
permits leading a life entirely like in the countryside. They were therefore very happy on
coming to know we would be staying here. They also have good friends here. We grownups would have been sorry that we could not have taken Hainberg with us!"On 3 December 1923 Prandtl finally rejected the Munich offer. The Directors of KWG
had been on the look-out for a private donor in order that the plans for the new institute
did not have to be dropped. The Director-General of the company W. HoeneAktiengesellschaft was in a position to place funds at the disposal to help put up the newbuilding. One half of the sum necessary was approved by the new finance minister
Luther.

73

74

L.Prandtl's hand-drawn sketch of Kaiser-Wilhelm -Institut für Strömungsforschung (Kaiser Wilhelm Institute for
Flow Research ), inaugurated in 1925

9. Building up of the Institut and new projects
All the work that Prandtl had put in by way of building up did not have to be given up
now. Even during the phase of construction work on the buildings the research work at
Göttingen went on further without interruption with the help of Assistents well acquainted
with the work and with reliable technicians. The new building was supposed to provide
an opening for research (work) that was less oriented towards a specific purpose,
independent of the other more application oriented Research Laboratory whose task was
to investigate into the flow characteristics of airplanes, turbines and other models. In theyear and a half that followed, during which the Kaiser-Wilhelm-Institut was established,
extraordinary commitment was demanded of the personnel of the establishment. But thework of planning and the progress made at work, generated the enthusiasm for everyone
to apply himself with joy and eagerness at work.
Ingenieur Walter Müller told me: "There were no fixed times of work then, neither forme nor for others". It was understood and natural for him to spend the whole of theevenings at the institute when the measurement data had to be reduced or whenexperiments had to be set up for the next day. 'There was also no specialization. Everyone
could do everything.'
In the meantime the research work did not come to a standstill. New but importantsecondary problems concerning turbulence had arisen in boundary-layer theory. A few
articles of Prandtl on the new subject of turbulence appeared in different scientificjournals. Thus, simultaneously with the building up of the institute, there was continuous
progress on the theoretical side, and in fact on new projects.
One of these new projects was the Flettner-rotor ship, an especially interesting project
under the scientific supervision of the Assistent Dipl.-Ing. Jakob Ackeret (from
Switzerland), which culminated in 1924 in a technically successful product. This was theso-called ''rotor ship'' (Rotorschiff). Precise studies of the performance of rotating
cylinders, built as rotating towers on a ship's deck and exposed to the wind, had shownthat they generate a larger driving force than the usual sails made out of fabric. The
engineer Flettner, inventor of the rotor ship, brought his project to a successful end withthe help the fluid dynamists. The prototype was built at the ''Germania'' docks in Kiel.
Prandtl was often requested to come over there to give his expert's opinion on thefunctional efficiency of the ship. After it had proven itself in several trial cruises, the ship''Buckau'' could be employed in coastal waters. Note made by Prandtl on 12 November
1924: "Cruise on the Buckau, with Prince Heinrich, Busley and many others, toEckenförde.''My husband remembers that he had seen this unique ship that was gazed at withadmiration by everyone on the section of the river Elbe known as Aussenelbe, and that its
singing monotonous sound echoed far across the river.
December 1924, Prandtl wrote a newsletter for circulation:

75

"Regarding the invention of the Flettner sailing boat we have received letters of different
types in such large numbers that it was impossible to reply promptly. A few typicalquestions have been answered below. We request you to be satisfied herewith.
1) There are no publications by us up to now on this subject. However the following
articles will appear in the beginning of next year: One by Dipl-Ing. Ackert in Zeitschrift
für Flugtechnik und Motor-Luftschiffahrt, one by Dr. Betz in Zeitschrift des Vereins
Deutscher Ingenieure, and one by Professor Prandtl in 'Naturwissenschaften'. Besides,
the publisher 'Vandenhoek und Ruprecht' in Göttingen will bring out a brochure titled'Das Rotorschiff' authored by Herr Ackeret.
2) Regarding the application of the rotating cylinder in other cases, it may be noted thatthey are meaningful only where, as in a sailing boat, one is interested in having surfacesof smaller size than at present. In all other cases, as in airplanes, windmills etc., the winglike shapes presently in use are to be preferred due to their lower aerodynamic drag.''
Shortly before this, on 17 November 1924, Prandtl had given a lecture on the rotor ship at
the Göttinger Physikalische Gesellschaft (Göttingen Physical Society) [30].
In his preface to the brochure by Jakob Ackeret titled ''Das Rotorschiff und seine
physikalischen Grundlagen'' (''The rotor ship and its physical foundations''), Prandtl
wrote: ''The sensational success of the peculiar Flettner wind-power propelled boat hassuddenly drawn attention of the public at large to some facts that, until then, used to be
discussed only in a small circle of specialists with technical knowledge. An explanation
was sought as to how it is possible for a relatively thin and rapidly rotating cylindrical
tower to replace a sail with an area ten times as big.''
This brief note written for the layman explains the phenomenon perspicuously, although
it pre-supposes a certain understanding for physical relationships.
The invention was explained at a public lecture in Göttingen to the interested public. The
announcement: Stadtpark, Friday 20 February 1925, 8 o'clock. Lecture with slides byProfessor Prandtl on the Flettner rotor ship.
From the (local) newspaper Ortsnachrichten, Göttingen, 22 February 1925:''Yesterday, Professor Prandtl gave a talk on the Flettner rotor ship in a well attended
auditorium. Due to the very nature of the subject, the lecture, for most part, wasacademic. But it was delivered in such a way that the layman could follow the chain of
events occurring. It was extremely interesting to listen to a person who was instrumental
in turning the Flettner invention into reality, talk on how the result, which justifiably
created so much sensation in the whole world, was achieved by scientific foundation anddiligent study of the characteristics of air flow. The speaker substantiated his statements,
and was interrupted by applause, through projected slides. At the end of the talk, Prandtl
raised the question of the rotor ship becoming important for navigation. He answered the76

question by saying that the usage of the rotor ship would depend upon economic
considerations.''
However, hopes that were nourished with the coming of this type of ship---there were
expectations of shipping cargo becoming cheaper---were not to come true.
It was due to economic reasons that this invention did not succeed in practice. The
expenses necessary for maintenance of the engineering on board were so high that, forinstance, fishermen were not willing to invest in the same. Since, without regularsupervision by a mechanic attending to the smooth functioning of the high speed rotors,
the boat could not undertake trips of a longer duration reliably.
Today, the energy saving principle of the rotating towers has returned under the nameturbosail. Recently the oceanographic researcher Jacques Cousteau was on a research
expedition of two and a half years with such a wind-powered boat. In June 1985 he wasin the port of New York.
Another area of research pursued by the research laboratory at that time was the drag ofland-based vehicles. It commenced with a set of experiments aimed at reducing the
aerodynamic drag of locomotives in order to save energy. The wind force wasinvestigated on a 1:25 scale model with its front and sides shielded. The calculations
showed that in this case, at a train speed of 90 km /hr a saving of coal of 80 to 100 kg perhour could be attained [23]. These experiments were later continued successfully with apowered rail-car stationed in Göttingen and built according to the models tested.
Sometimes we children were taken on the testing track to Northeim.
In the meantime the work of extending the laboratory had been completed. Ingenieur W.
Müller still remembers from those days of a small mishap that occurred shortly before its
inauguration. The floor of the director's office was covered with tiles of (synthetic)
rubber in a black-and-white chess-board pattern made by the company W. Hoene. Whenhe saw it, Prandtl didn't like this flooring at all. He said: '' Perhaps this pattern would suitin a butcher's shop.'' He stood at the door and said: ''I do not go in here!'' The flooringtiles could still be changed. Beige-marmorated tiles were chosen and the flooring wasdone in time for the ceremonial act.
The inauguration was festively celebrated on 16 July 1925 at which the then President ofKaiser-Wilhelm-Gesellschaft (KWG), Adolf von Harnack, was also present. At thisfunction W. Hoene was awarded an honorary doctorate (Dr. h. c.) as planned.
At this juncture I wish to draw the reader's attention that it was quite in keeping with thetradition then to bestow such an honor on an industrial magnate. For instance, Klein was
basically of the opinion that, if he wins over a rich industrial magnate to donate money to
the University for building a new institute, he - the donor - should be given a degree ofhonor for his merits in supporting science. Although in the meantime a decision was
taken against this practice in a faculty meeting, members of the same faculty voted with amajority in favor of granting the honor to Hoene who had made a demand of the same.

77

President von Harnack handed over the new Kaiser-Wilhelm-Institut to Professor Prandtl
with the following words:"We look for a good researcher meticulously. When we have found him, we direct
streams of goodwill towards him, procure funds for him as generously as possible, andleave it to him to do what he considers right."

7810. The new Kaiser-Wilhelm-Institut
As already mentioned, the scope of duties for the laboratory had substantially widened.
Whereas in the war years it served primarily the purpose of airplane related
investigations, it now addressed questions of wind-induced forces on iron girder bridges,
electrical power transmission cables and high-rise buildings, in order to learn to build
these structures with greater stability and thus protect them from damages due to storm.
A journalist with insight wrote: ''The building codes now in force are obsolete andurgently need revision.''
The new tunnel of four meters test-section diameter permitted tests with larger models in
the windstream. For instance, it was possible to suspend a full-sized blade of a wind-mill.
The question addressed was how its shape could be improved in order to better utilize theenergy in the wind. With the large number of research problems on which now work wasgoing on in the different buildings of the Institut, it now became necessary for two
directors to be in charge, Ludwig Prandtl and Albert Betz. The latter became the deputy
director of the Institut and took over as the head of the Aerodynamische Versuchsanstalt(AVA). Prandtl was in overall charge and attended mainly to work in the new Institut für
Strömungsforschung. In November 1926 the personnel strength stood at 55.
Visiting colleagues were shown around the new laboratory and offices, and signed theirnames in the new visitors' book in the Director's office. My mother and we children werealso permitted to go around the premises, and we saw with admiration the beautifulmodels in the wind tunnel. We were shown a new experimental facility that we liked very
much: the rotating laboratory. It was meant for model experiments attempting to simulate
on the laboratory scale the large-scale fluid motions on the earth. In the facility fluid flow
behavior was investigated when there was rotary motion [25]. For us children it was aspecial attraction to board the rotating platform and be taken around a few times like on amerry-go-round. Dr. Busemann, who was conducting scientific experiments in thisfacility, was kind enough to let us ride on it many times. During the rotary motion in thefacility, one was completely isolated from all external surroundings by the walls. The
thinking was that the experience of dizziness is mainly due to the motion past near-by
stationary objects. But we were in fact not entirely free of dizziness even in the closed
laboratory when the rotational speed was high; neither was Dr. Busemann, although he
had adjusted himself to it by incessant practice. Our father, who had also boarded with us,
explained to us how the centrifugal force hampers the movements of the body to one side
and eases them on the other. We tried our utmost to twist our arm against the direction of
motion; but in vain, until the speed of rotary motion was lowered. Happy and enriched bythis experience we finally disembarked from the facility. We then went into the buildings
where the wind tunnels were situated. With Father taking us around, we quickly felt athome in the big halls. All the wind tunnels were surveyed in order of their size. Father's
desire to entertain us children was really touching. Another helpful Assistentaccompanied us to the control panels and switched on the blower of our choice. It was an
exquisite experience to stand in the open section of the tunnel with hair blown off andskirts fluttering in the wind. One could imagine standing on a ship and the fresh windblowing in the face. It was exciting. Then, all of a sudden the wind got so strong that one

79

could cross the tunnel only with difficulty. We could feel that a little more force exerted
by the wind would make it impossible for us to keep our feet on the ground, and wewould be blown off against the wall. Finally we visited the largest wind-tunnel of thattime in which various models were held suspended by strings. They were taken out for awhile and the facility switched on. This time we were contented with the magnificent
noise that the blowers could generate at full load. The forces set free were calmed down
and mastered again quickly. How much did we after all like this impressive noise
generating facility!
The next day I told my friend Lilli Misch about this unusual entertainment; and since ourprimary school on Bürgerstrasse was not very far from Böttingerstrasse, we, the two
small girls, decided to go on a merry-go-round trip directly after school closed for theday. But the enterprise did not succeed. Having come there, I told them at the gate that I
wanted to see my father. He was not in his (Director's) office, nor in his Institut, but in adifferent building. Someone was sent out to look for him, and it took a long time for him
to come. He smiled with embarrassment when he saw us, but sent us home firmly. He did
not show any sign of irritation on our pulling him away from work, but I had theexperience of his not being available for me on sudden call, and that was difficult tocomprehend. My friend, who lives in America now, also remembers our plan very well,and the scene that put everything to an end. Had my mother known of our plan, shewould have obviously held us back. Never did she call her husband in the Institut from
home, so much did she hold his working world in respect. She knew that he wasextremely busy, and that he invested all his capacity for work for the cause of theprosperity of the Laboratory and to its various research tasks.
Every year there was a party organized for the staff of the Institut personnel at a guesthouse in the countryside. The young people liked the opportunity of entertainment at theevening dances. Before that the participants thought up and arranged exciting
amusements through all kinds of gags. Once, in order that the various items in the
program may proceed in an orderly manner, they were laid out on different tables.
However item 3, intentionally left out in Prandtl's list, had the entry: ''Prandtl plays with a
toy''. Someone was required to bring in and place on the table a kind of technical toy
when Prandtl was giving his little speech. As the air was thick with suspense, the gag
succeeded: Prandtl, attracted as always to unknown objects, reached for it spontaneously
and began to play and experiment with it. In the meantime, everyone had come over fromthe other tables to watch from close quarters. Prandtl then noticed that his love of playing
with toys had been exposed, and he ended his involuntary performance with a smile.
In spite of his busy program of work, those were years of great happiness for the head of
the Laboratory. Another incident from those days has been put down on record by Frau
Margarethe Winter, nee Weppner, in Göttinger Monatsblätter:''I can recount a nice conversation I once had with the renowned Professor Prandtl. By
chance, on a nice spring day, we left the former AVA together. Prandtl felt like taking asmall walk, and asked me if I would accompany him for some distance. We walked
together, and he noticed that I had a minor walking disability: I had just had an80

inflammation of the walls of the vein (phlebitis!). He said spontaneously, that that was
really a matter of ''fluid flow'' in the blood vessels; he wanted to think it over, and perhaps
he should sit together with a doctor and discuss it. But we never came back to the subject
again.''

8111. Journey to London
An event of special significance in the year 1927 was a journey to London where Prandtl
was to deliver the Wilbur Wright Memorial Lecture at the Royal Aeronautical Society.
Roughly a year and a half earlier he had begun to learn English under private tuition,
supported by his wife Gertrud who spoke English well. It was already a sufficienthindrance for him that he had to get the publications from England and America
translated, although he understood the technical terms. His very capable teacher, Beatrice
Dammers, daughter of an Englishwoman, supported him with her best efforts. It issurprising how, with his heavy load of work, Prandtl mastered sufficiently well and insuch a short time, a language that he had not learnt at school as to deliver his well
prepared lecture in English in London.
Newspapers in both England and Germany followed his journey closely. For example,
The Daily Chronicle said on 9 May 1927:''England to honor German Professor. A quiet retiring German, who cares nothing for
ceremony or fame, but who is acclaimed the greatest living authority upon aerodynamics,
is coming to London this week to receive from England an air honor, which in all thehistory of flying has only be(en) given to six men. This famous scientist is Professor L.
Prandtl of Göttingen University and the coveted distinction to be conferred upon him is
the Gold Medal of the Royal (Aeronautical) Society.
Previous recipients have been:
1909 The Wright Brothers
1910 Professor Chanute
1915 E. T. Bust and Professor G. Bryan
1926 Professor Lanchester"
The announcement proclaimed that Prandtl would be receiving the extraordinary andhighly esteemed medal in person.
The flight Hannover-London, on a Deutsche Lufthansa aircraft, was Prandtl's firstjourney by air; and for him a very special kind of experience. He made a record of his
observations by noting down key words along with the time:''Thursday, 12 May 1927:
4.58 Rotterdam, the Rhine estuary, Sun
5.14 on the sea, ebb tide
5.25 big port city
5.56 sea channel with city
6.06 big seaport (Dunkirk)
6.20 on the sea, very hazy
6.27 last land across, aircraft is very steady in the air82

6.35 land in sight, port, cliffs.''
The Göttinger Zeitung said on 14 May 1927:''Professor Prandtl in London
A report from London says that Professor Prandtl from Göttingen University arrived
there by air the evening of day-before-yesterday. Professor Prandtl will be given thehighest honour that British aeronautics can bestow, viz. the Gold Medal of the Royal
Aeronautical Society.''
The Daily Telegraph, 14 May 1927:''Professor Prandtl arrived in London by air on Thursday night. In a conversation
yesterday with a press representative he said: 'It is a great honor the Royal AeronauticalSociety is about to bestow on me, and nobody realizes it more than myself. If I have beenable to throw new light on the science of aeronautics, that in itself is sufficient reward forme. The Gold Medal of the Royal Aeronautical Society is more than I ever dreamed I
should receive, even in my most ambitious moments' ''.
On Monday the 16th May Prandtl gave the important ''Lecture'' [32].
On 17 May Colonel Forbes-Sempill (pilot and aviation expert), President of the Royal
Aeronautical Society wrote to Prandtl:''Dear Professor Prandtl
First of all I want to take the opportunity of thanking you in the most sincere manner
possible for your wonderful Lecture, illustrated by the most remarkable series of slides
and cinematograph films that have ever been the good fortune of the Society to see. Your
Lecture has aroused the greatest possible interest and we are already receiving demands
for the Society's Journal in which it will be reproduced.''From the ''Morning Post''''Colonel Master of Sempill, Chairman of the Royal Aeronautical Society, said yesterday,'but we have chosen a German this time because Professor Prandtl is, in our opinion, andin the opinion of all people who are competent to judge, the greatest authority on thescientific side of aeronautical science. He has particularly distinguished himself by
propounding what is commonly known as the Prandtl boundary layer. By his years ofexperimenting he has given us an insight, denied to the greatest men of science in thepast, of what happens to the air surrounding an aeroplane in flight.''
An article in the Göttinger Zeitung of 18 May followed:''Wolff's telegraph office reports that Professor Prandtl of Göttingen University gave alecture on Monday in London at the Royal Aeronautical Society. This received special

83attention since the German scholar, a leading authority in this branch of science
according to the unequivocal opinion of all British scientists, was the first person who
was not either an Englishman or an American to be invited to give a Wilbur Wright
Memorial lecture. The Royal Aeronautical Society emphasizes in its invitation to thislecture that, just as the Wright Brothers brought manned flight into the realm of practicalpossibility for the first time, Professor Prandtl has made it possible to understand how
and why the air sustains aeroplanes in flight. As already announced, Professor Prandtl
will be presented today with the Gold Medal of the Royal Aeronautical Society that has
up to now been awarded only to six men.''
The rather long list of reports that I have included here on this special honor to Prandtl
should be understood against the background of the situation prevailing during thosepost-war years. The majority of Englishmen still regarded the disagreeable German morethan just censoriously. The fact that Air Vice Marshal, Sir Sefton Brancker, in his
welcoming address at the Memorial Lecture, referred to Prandtl as 'an important citizenof a great nation', made him (Prandtl) conscious that he was not just facing scientists, but
had to represent as a German his mother-country that had been humiliated by the
victorious powers of the world war. This recognition was registered with gratification in
his home country.
It is appropriate to add here that Professor Lanchester from England, an earlier recipientof the same award, had addressed the same problems as Prandtl. In order to clear any
doubts that could possibly arise on Prandtl having worked out his wing theory on his
own, Prandtl said during his talk in London:''In England you refer to it (the wing theory) as the Lanchester-Prandtl theory, and quite
rightly so, because Lanchester obtained independently an important part of the results. He
commenced working on the subject before I did, and this no doubt led people to believethat Lanchester's investigations, as set out in 1907 in his ''Aerodynamics,'' led me to theidea upon which the aerofoil theory was based. But this was not the case. The necessary
ideas upon which to build up that theory, so far as these ideas are comprised in
Lanchester's book, had already occurred to me before I saw the book. In support of thisstatement, I should like to point out that as a matter of fact we in Germany were better
able to understand Lanchester's book when it appeared than you in England. English
scientific men, indeed, have been reproached for the fact that they paid no attention to thetheories expounded by their own countryman, whereas the Germans studied them closely
and derived considerable benefit therefrom. The truth of the matter, however, is that
Lanchester's treatment is difficult to follow, since it makes a very great demand on thereader's intuitive perceptions, and only because we had been working on similar lines
were we able to grasp Lanchester's meaning at once. At the same tine, however, I wish to
be distinctly understood that in many particular respects Lanchester worked on different
lines than we did, lines which were new to us, and that we were able to draw many usefulideas from his book.''
Many years later, in 1947, Prandtl expressed himself on this problem again [31]: ''Perhaps
the observation is not without interest, that even here it is a contradiction that stimulated84

my first occupation with the subject of wing theory. I am referring to the misleading
concept of the vortex system of a (lifting) wing in the otherwise laudable book of F. W.
Lanchester (Translation by C. and A. Runge, 1909).''Prandtl stayed for a week longer in England and accepted many different invitations. He
also visited his English colleague Professor G.I. Taylor in Cambridge, with whom he had
shared many years of warm friendship.
Many congratulatory greetings were awaiting him on his return. At the end of thesemester, the students honored him by taking out a torchlight procession.
From Göttinger Zeitung of 14 July 1927: ''Torchlight procession of the student body.
Honor for the aerodynamicist Professor Prandtl, who was recently awarded thehighest honor in London for his achievements in aeronautics. The procession moved
along to Calsowstrasse 15, where a festive ovation was staged. In his address, a
representative of the student body praised the achievements of Professor Prandtl inaeronautics, and through them, in the cultural attainments of mankind: ''We owe ourknowledge of flight to his research. The world looks towards Germany, towards oursmall Göttingen, towards our distinguished scholar. The Student Body of Göttingenhonors the teacher by a thundering Hoch!' The air was filled with the sound: 'Vivant
professores!'In his address of thanks to the student body, Professor Prandtl, with the modesty of a true
scholar, tried to present his achievements as if they were not of any extraordinary value.
The credit, he said, should go chiefly to Professor Felix Klein, to whom we owe the
Aerodynamisches Institut. Besides, the contribution of his (Prandtl's) Mitarbeiter had
been substantial. But, much as we honor Prandtl's modesty, we still adhere to the viewthat the major share of the credit belongs to him. Just as the artist and the good violin go
together, so do Prandtl and the Aerodynamisches Institut---to perform what has in reality
been performed. Professor Prandtl ended his address by a Hoch to the German Fatherland (Vaterland). The National Anthem was sung, and the procession went to
Theaterplatz where the torches were huddled together.''I still remember this evening well. I had been probably already asleep for a while when I
was fetched to the living room. The large group of torch bearers presented a wonderfulsight from the open window above. My father stood at the middle window, with theupper part of the body slightly bent forward, and holding on to the window frame withoutstretched arms.
The student who addressed the gathering then was Gustav Messmer. Later, he did his
doctor's degree with Prandtl. In the year 1939 he was 'called' to the professorship of
applied mathematics at the Technische Hochschule in Darmstadt, where he stayed until
1949; he was appointed as the Rektor of Technische Hochschule Darmstadt from 1947 to1949. In 1952 he accepted an offer from Washington University in America, where hedied in 1981.

85

There was a change of staff at the Institut that I should mention. In a room next to the
Director's office there was a new secretary sitting at the typewriter. She had started
working on 19 May, the very day her new boss returned from London. It was Fräulein
Eleonore von Seebach. She had come to know about the vacancy for the secretary's postthrough friends, as it used to happen generally in those days. Fräulein von Seebach told
me that right at the time of introduction, Prandtl asked her to take down a dictation toconvince himself that the young lady had the ability he expected of his secretary. She wasthen asked to report for duty at the appointed hour for a probationary period. She has
been there since then for 43 years as a private secretary, continuing even after Prandtl's
death, and serving his successors as an experienced secretary.
She told me that she remembers the early days very well. Prandtl dictated a stenogram,and did not abstain from making corrections of style in the finished draft of the letter
before it could be typed. Correspondence was never left unattended, and replies, to thepoint, were written promptly. He was rather dissatisfied when he was not understood
immediately. He could not stand dim-wittedness, but was very patient and calm while
dictating to her. Fräulein von Seebach adjusted herself admirably to him so an excellent
understanding at work developed between them. Beyond these duties she also kept
herself available for typing scientific articles for the Assistents. She typed Prandtl's book
Führer durch die Strömungslehre [27] from dictation. She also remembers theegomaniacal letters Prandtl used to receive from inventors, to whom he replied withpatience and clarity, and who, out of disappointment at not being recognized, kept
stubbornly presenting their ideas again. They would often not understand the Professor's
chain of reasoning showing the flaw in their thinking. And he then had to frame the proofof their false conclusions in even more detail.

8612. Journey to Japan
When my father was making preparations for the next big journey, we, his daughters,
now 12 and 14 years old, actively participated in the task. It was a journey round theworld that was to last for half a year. The main reason for the journey was an invitationfrom Japan. A congress was to be held in Tokyo. Following the congress, a journey
through America had been planned, during which Prandtl wanted to visit different
universities.
Big trunks for overseas travel arrived at our house, and my mother took care of buying
new clothing. She had really wanted to travel with her husband on this interesting
journey, but the thought of leaving us alone outside her care for so long was something
she could not live with.
Travel to Japan in 1929 was an adventure far more sensational than it is now. Today aplane journey to Japan is nothing unusual, but in earlier days, one had to travel over land
across Russia, as there were no flight connections over such large distances.
In his travel kit there was a Leica, which was the best camera in the world those days. He
thought he would awaken his memories later by looking at the pictures. On 13 September
he left Göttingen and traveled eastward. My mother received more than 70 letters fromhim during his long absence from home. He numbered them all serially right from the
beginning.
Prior to writing anything in particular from these letters, however, I wish to quote
excerpts from a newspaper article in which my father, having just returned home,summarizes his impressions of the journey to the journalist.
March 1930 - Interview with Professor Prandtl:''Impressions of and experiences on his journey to Japan and America: As has alreadybeen briefly reported, the well-known Göttingen aerodynamicist, Professor Dr. Prandtl,
returned to Göttingen on 5 March, after traveling around the world for almost half a year.
In an interview kindly given to our representative, Prandtl gave an overview of his travel
impressions that are summarized in the following:'The goal of my journey that took me through Russia, Japan and America, was reallyTokyo. The World-Engineering-Congress held a conference there at the end of
October/beginning of November last year, in which I was specifically invited toparticipate. It was dear to me that I could not refuse this opportunity to get to know othercountries and, wherever possible, to pursue general and subject-oriented scientific studies
there. The journey became correspondingly longer. The journey started on 13 September,and first took me by train to Moscow. On the program in the Russian capital there werevisits to many different institutes. The standard of the equipment in these laboratories wasamazing. At present there are new experimental facilities. In spite of the difficult

87

situation, the Soviet government is deeply involved in everything that serves to further
technology.
“From Moscow it was a ten-day long journey towards the Far East by the trans-Siberian
railway. Even this rail route left an impression of sturdiness. The tracks, the cars and themachines were all in impeccable condition, and we arrived in Vladivostok with only athree-hour delay. Originally I had planned to travel through China, but due to the SinoRussian dispute this route is blocked.
Now to Japan: This is a country whose rapid advancement is clear in every way. An
enormous industrial development is noticeable in the whole country. In no other country
has the installation of electrical power been managed as it has been here. Every village inJapan has electricity. This development is all the more amazing considering that six years
ago there was a big earthquake that had a devastating effect on the country. Big cities
have either been entirely or are being rebuilt as we speak. Japan is a country whose native
art is blossoming to the full.
Everywhere there are lovely objects for sale, and they are truly lovely.
The Congress itself, which was the real goal of my journey, was well organized by theJapanese. The number of participants was large: from Germany 30 representatives had
traveled to Tokyo, and in addition there were about 30 engineers who were working inJapan. Regarding the hospitality of the Japanese, there can be nothing but praise. The
congress participants were treated to lunches and dinners again and again, were much
pampered, and there were many festivities held.''
At the time of the Congress there was still the old Nippon. This changed only at the
beginning of the thirties when the modern outlook of the European West started toinfluence the whole life of this Island kingdom in the Far East.
'The scientific institutes made a good impression. Aerodynamics is also highly cultivated,
and there are more wind-tunnels than we have. Apart from the special scientific studies, I
had a four-week long stay that was devoted to getting to know this interesting country.
'The journey then took me across the ocean to America where I spent two and a halfmonths. Of course I was particularly interested in their aeronautical institutes.
'In general, at the American universities, I did not find many more facilities than we havein Göttingen, but only the facilities are available in a larger number of universities. There
are special laboratories for aeronautics in many universities. They have mostly windtunnels that are both the same size as in Göttingen and smaller. The National Laboratory
in Langley Field near Washington (DC) is superb, and excellent work is done. Their
facilities surpass what we have in Europe. For instance, there is a wind-tunnel with a test
section area, the diameter of which measures six meters. Full-scale aeroplanes can beinstalled in the test section, which means that better studies on propellers and engines canbe conducted.

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'The landscapes? Of course they were all very different. In the Siberian steppe there wasnothing but grass, and then again forests of low birch trees. In the American steppe thescene is the same, only with other kinds of trees. There are expanses where many acres of
pasture land can provide fodder for only a single cow: grass struggles to grow there.
Japan with its rice fields and colorful temples is of course entirely different.'
Loving hands had decorated the door of Prof. Prandtl's office with a wreath when hereturned, and the room in which he received me was full of colorful flowers. And
certainly, this honor gave him the same joy, or perhaps even more, as the floral presents
bestowed upon him on his journey.'' (End of the report on the interview)
This experience of a round-the-world journey seems to me to have been of very special
significance in Prandtl's life. It was a period when he often encountered the unusual,gathered many impressions, made manifold observations and mused over them- so muchso that I wish to pick up the course of his journey again through his letters.
The first stop on his outward journey was in Berlin, where he met Professor Nägel from
Dresden. Professor Nägel was also a participant in the Congress, and the two of themwent on to make further journeys with one another.
15 September 1929:''At the end of a 40-hour railway journey we arrived at 11.30 in Moscow. We were
photographed and filmed as we got off the train. After that we were taken by car on ashort round-trip with splendid roadside views: a propaganda procession with school
children carrying slogans on red sign-boards; then to a church (Erloeserkirche) where
there was a festive mass and the choir singing was going on, then further around the
Kremlin with its many towers, and finally to the hotel, where I have a splendid room witha bath. Today's reception and the first impression of the city with its kaleidoscopicallychanging views will probably stay in my memory for ever.''
He gave three lectures in Moscow. He was invited to meet the German Ambassador,
attended a performance of the Bolshoi Ballet, visited the Tretyakov gallery and theMuseum of the Revolution.
On 29 September the long journey across Siberia started aboard a sealed railway train.
29 September:''In the early hours of this morning we crossed the Ural mountains, a flat elevation of
about 400 meters, mostly covered with birch wood trees.''
2 October:89

''Now we have been on board the train for 4 times 24 hours, and will have soon
completed one half of the train journey. The clocks show it to be already 5 hours ahead of
the time in Germany. Around 10 o'clock yesterday evening, we crossed the Ob river near
the city of Novosibirsk. It is a huge torrential stream, with nothing like it in Germany.
The thousand lights of the largest city in Siberia and two brightly lit steam boats cast theirreflections in its waters.''
2 October:''This morning we saw mountains in the distance, not unlike in the Black Forest. The
woods, with the golden yellow of larches and the green of the pine trees, and the grayish
yellow of the withered grass, are very beautiful, particularly in the early morning red of
the rising sun.''3 October:''Today's experience was the Baikal Lake. The train moves along the lake for about six
hours. Unfortunately it was one o'clock at night when we came there. We were therefore
in a position to enjoy the landscape only from a quarter past 5 up to a quarter to 7 in themorning, at sunrise. There is surf on the lake with big frothy crests. The dark grayish
green water, the sky with dark gray clouds, the mountains on the shore, all shone with theearly morning red. We slept again from 7 to 9.''
6 October:''This is the last postcard from the Siberian railway. At 2 in the afternoon today wecrossed the Amur river over a bridge that measures more than 1 km. From half past 2
until 3 we were in Kabarovsk, an important trading city. This region is quite charming,the blue mountains on the far side already belonging to China. One sees many Chinese
faces at the railway stations, mostly workers, some in European clothing, some inremarkable rags. By the way, the entire journey from Moscow is 9330 km.''7 October, Vladivostok:''The hotels are overcrowded, since they were not prepared for the heavy flow of traffic
going through here because of the blocking of the Chinese railway. We were extremely
lucky: Nägel found the German Consulate's car. After a bit of a wait, the secretary of theConsulate to whom we had been asked to convey greetings from the Russian Embassy in
Moscow met us, and he got our baggage transferred to the Consulate first. While we weresitting there, we were pleasantly surprised to be invited by the Consul's wife to stay withthem.''
From Vladivostok it took them several days to travel by boat to reach Japan. On 11
October they were received hospitably in Kobe. Professor Wieselsberger, who had beenan Assistent in Göttingen, and Mr. Takao, Director of an airplane factory, had come on
board to greet the two visitors.

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12 October:''Something very special today: Mr. Takao invited us to take part in an excursion withsome Japanese ladies picking and eating mushrooms. For this purpose, one rents an areain the hills near where the mushrooms grow, which is cordoned off so that others do notsteal the mushrooms. The whole party drove over in four cars. To start with, on a riverbank where the cars met, there was an elaborate exchange of greetings of the men
amongst themselves, with each bowing three times. Thereafter the party drove further bycar, and then walked for a quarter of an hour to a small hillock on which there weremushrooms (of a different kind from ours). Everyone got a basket for collecting themushrooms. In the meantime, small cooking ranges made out of potter's clay had beenheated by charcoal. Chicken, different vegetables, bean curd and eggs were all cooked onthese ranges, laid out on a table-cloth, eaten directly, then roasted again. The food was ofcourse eaten with chop-sticks, which everyone likes. Then there was sake to drink andlots of photographs were taken. All in all, quite a charming experience. In the afternoon,
we visited an airplane factory.''
16 October:''Drove by car to the park-villa of the airplane factory owner outside the city of Kobe. We
drove there by car. The house was in a beautiful garden with a lake and bridges, a small
hillock and several small cottages for drinking tea. At first we took the main house for a
big tea room, but we were assured that the family really lived there. The total absence ofany furniture is very queer. There are only pillows and arm-rests, and one sits on thefloor. You take your shoes off in front of the house. At first tea made out of seaweed(tang) was served in the garden: then ceremoniously we washed our hands, then waited inanother pavilion until the gong was sounded, and were finally led into the main house by
its owner, to be seated on the pillows ( arranged in the shape of a horse-shoe). The
women provided things to eat on a small table in front of us, but did not join in eating.
On the next day we visited Osaka (45 km from Kobe): a very interesting city with a fort
and temples. Invitation by the Consul-General in the evening. Today a day of rest, which
was also very much needed.''20 October:''Finally we are in Tokyo. The last two nights we stayed in Kyoto, in the famous MijakoHotel, a true spa hotel built on a hill. The view reminds one of Baden-Baden, but themountains are more beautiful. In Kyoto there are wonderful temples, three of which wevisited (one should really visit at least ten). In the evening, a stroll through the shoppingarea, colorful beyond imagination. Yesterday we were at the temple-city of Nara, a placeof pilgrimage with Shinto and Buddhist temples, all in a wonderful park, where packs oftame deer roam about. Here there is a huge bronze statue of Buddha that seems gigantic
in the dark temple hall with a high ceiling.

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Tomorrow, the day-after-tomorrow and the next day from 2 to 4 o'clock my lectures [38]:on Thursday at Baron Shiba's, who is the Director of the Aerodynamics Institute.''3 November:''The invitations continue coming. I do not keep count of them any longer. All I can say isthat we have been invited to tea in splendid gardens, to theater performances, lunches,
dinners, balls, etc., every event outdoing the other in winning ways. The lectures haveentirely receded to the background.''
9 November:''The Congress is now over, and this morning we traveled down to the temple city of
Nikkio. A richness of form and color beyond imagination. The big buildings are riddledwith ornamental pieces, small figurines no bigger than a hand in size and which, each andevery one, have been worked out so carefully and with attention to the minutest detail.
Everything is in red, green, blue, black. The temple beams are painted in red and arepolished. Tomorrow we are going by car up to a height of 600 m to see a waterfall and alake.''
11 November:''Yesterday we took Herr Nägel to the railway station. From now on I have to be on myown. He was, with his versatility and broad knowledge of languages, of much help andsupport to me.''On the following day Prandtl traveled eastwards. Subsequently, he was presented withfarewell gifts (a pin with pearls and landscapes painted on silk).
18 November on board the ship ''President Pierce'':''Yesterday was Monday, 18.11 and it is 18 November today again! We spent yesterday(the 18th) with Japanese people, while you were sleeping, and today (the 18th) with
Americans.
Today we had sunshine for the first time, and also a very beautiful sunset. Imagine agreen evening sky, olive colored at the bottom, topped with steel grey. On top of that itwas violet, and in the green stripes there were vermilion colored clouds. To the left of thisharmony of colors the sky was deep blue, lower down whitish, and brownish on thehorizon. Later the green turned to yellow and still later to red, and now the colors weresimilar to those we are used to. The starry sky looks very much different here, imagine
the northern sky without the great bear.''21 November:92

''The ship berthed for two days in Honolulu. We were greeted with Hawaiian music. I
walked over the landing bridge into the big customs hall, and was much surprised to bereceived by a gentleman who asked me if I was Professor Prandtl, and then garlanded mewith fragrant flowers placed around my neck. Here there are trees and shrubs blossoming
in all seasons, and how beautiful!---they are brilliant yellow, bright red, dark red, palelilac, brilliant reddish violet, all flowers unknown in our place; and a wide variety offruits. The main goods produced are pineapples and cane sugar. Honolulu is on the slopesof a giant volcano. The mountains forming the rim of the crater have very interesting
forms. I learned from my escort that I am invited to lunch the next day and that I am
supposed to give a small lecture there. My usual themes were all unsuitable for thispurpose, and so we agreed that I give a talk on gliding. We got into his car, and drove up
the mountain and over a pass to the other side of the mountain chain on the inside of thecrater. The mountain walls drop very steeply. The landscape is very romantic with theblue sky in the background. Then, at dusk we returned by a different route.
There were about 20 men at lunch. Beautiful club house, address by the presiding
gentleman welcoming me. My speech came next, the first time in English without notes.''When, after twelve days, the ship landed in San Francisco reaching American soil, there
began for Prandtl the American lecture tour that took him to many well known university
towns. A stay in Pasadena was followed by a few days in Urbana, after which he stopped
in Chicago, Detroit, Wright Field, Washington, Ann Arbor, New York and Boston,giving lectures in all these places. He also made sure that during the long journey throughthe rest of the continent he visited famous sight-seeing spots.
Accordingly, he visited the island of Catalina, and took a trip there in a boat with atransparent glass floor. ''One sees the underwater gardens, sea plants and many kinds offish. In contrast to the mainland of California, where there are only roads for cars and apedestrian in the outskirts arouses ''suspicion'' and is barked at by dogs, on the island,
there are even nice walks (more precisely bridle paths). Today I walked along one such
path which, on reaching the mountain ridge, suddenly exposed the ocean to view. In thefar distance, the Californian mountains are visible. The sun was close to setting, and thecalm and peaceful sea of the Pacific Ocean shone in the gold of the evening. Over that I
could see the blue sky covered with the light silky sheen of the clouds. On both sides ofthe pass, left and right, there was a small peak, and I climbed both.''During his stay at the Grand Canyon he writes in a letter to his youngest daughter:
27 December 1929:''It is now high time that I write to you for your birthday. I am sending you a small gift- abook with views of this wonderful region where I arrived today. Imagine a vast plateau
with pine trees on it, 2100 m above the sea---that is roughly the height of the Karwendel
peak. To the south, past the woods, you see the blue mountains. But there is more on theother side! A big river has carved out for itself a valley with a thousand branches, and thebare rocks are visible everywhere. At the top it is shell limestone, and lower down it is93red sandstone, the same as can be seen on the surface near Reinhausen and Bremke. And
then there are three or four other kinds of stone, all in horizontal layers. The river valley
lies lower than Mittenwald as seen from the Karwendel peak. The air is very clear, one
can see very far into the distance, and the shadows are almost sky-blue. In this setting
there are stones, white and red and gray and violet-brown in color. A wonderfulsymphony of colors, changing with the time of day, from hard colors in bright sunshine
all the way to soft tones in evening twilight. So much for the Grand Canyon. I think
Mother will give you a present from me from the Japanese chest.''In Detroit there was only a visit to Ford plant.
Detroit: 16 January 1930. Prandtl, carrying only a small suit case on this leg of thejourney, was picked up at the [Detroit] railway station by a friend who wanted to takehim by car to the hotel. But before that they stopped at a restaurant to have dinner
together. When they returned to the car there was a sad surprise in store, since thieves had
broken into the car and Prandtl's leather case had disappeared. This theft upset him agreat deal, for the case contained, besides his change for the night, the Japanese pin ofhonor and the 13 films, still to be developed, that he carried with him as a precious
souvenir of his travels. His personal experiences had been recorded on those films. With
the eye of a landscape painter at work, he had been looking out for worthy motives, in thequiet and joyful hope of having enough time during the long journey to view all kinds ofsights that he deemed worth seeing. The next day he had an announcement published in
the newspaper asking the return of at least the films in exchange for a reward,unfortunately in vain. The loss made him sad for a long time.
9 February 1930, New York:''On the first day, in the morning, I was ''Downtown'', the main business district. I saw thesky scrapers and the great bridges over the East River, and went to the office of
NordDeutsche Lloyd. There I was introduced to the director as an important visitor. He
enquired opportunely about the state of affairs in Russia and Siberia. In the evening I
went to one of the hundred theatres on Broadway to see a talkie - Disraeli! The actors are
excellently present, with perfect reproduction of voices and other sounds like walking,rattling crockery, fine music---everything utterly superb. [Note: Talkies had not yet beenreleased at that time in Germany.]
On Saturday afternoon, I was in the Museum of Natural History, a first class collection
highly worth seeing. In the afternoon, I was in the Art Museum , with many paintings by
Rembrandt, Frans Hals, Van Dyke and so on, Egyptian, Greek, Roman antiques, artifacts
from the Middle Ages and modern times, from China, Japan, India, Persia - anoverwhelming abundance of beautiful artifacts.''
19 February:''This is my last letter from this country. The lectures in Boston went off well. On
Saturday I was at Harvard University where I visited some laboratories. In one division I

94

witnessed films showing the growth of chicken embryo tissues, the division of cells, andso on. The glass flowers in the museum are wonderful. They are made out of glass innatural form and color, by a man in Dresden, but can only be seen at Harvard. ''On 1 March my mother went to Bremerhaven, happy to pick up her husband on his return
home, directly from the boat. There was so much to talk about then that we needed days
to share all that he had experienced. Reports, comparisons, and passing references to thevisit to Japan made during conversations remained a central theme at the table for a longtime after the return home. And there was a clear indication on how deep the impressions
were that this country in the Far East, with a very refined but entirely different culture,
made on our father.
Children retain in their memory a vivid picture of the themes and objects that recur again
and again in their parents' conversations. And I summarize here from memory some ofthose impressions of Father's Japanese experiences.
I believe that the behavior of the Japanese among themselves impressed my father the
most. He said that noisy or crying children were not to be seen there. In their daily life,
the Japanese came into contact with each other in a friendly manner. The modesty andself control acquired by virtue of their upbringing has become a part of their life thatstrikes us as especially courteous. Japanese people love giving presents, always tastefulobjects offered with the utmost humility. This all serves to demonstrate the loving
attitude they exhibit in their relationships with other human beings. He especially praised
their noble hospitality. Their pronounced sense of cleanliness contributes to an outsider'sfeeling at ease. Everywhere one notices the unusual diligence of the Japanese.
For us, the Japanese objects he brought with him---two kimonos (tied around the waist
with obi), wooden shoes, stockings lined with cloth, small hairpins, and of course several
pairs of chop sticks- all these allowed us to establish our own intimate relationship withJapan.

9513. A day at home again
Now our home had again a pivotal point, and we knew ever more than before the extent
to which our father's nature set the course. The old habit of going with my mother toHainberg on Saturday afternoons was continued as a matter of course. After the stop forcoffee my father was often disposed to continuing his walk alone through the woods. He
took small unknown trails, of which there are many in the surrounding woods, always
with some special goal, whether it was reaching a beautiful view point or a spot with rare
flowers that had not been discovered yet by the people of Göttingen. Sometimes I
accompanied him on these ''deer-stalking walks'', and he explained to me untiringly agreat deal about plants, soil constitution and landscape. With his wide knowledge, he
could not always put himself in the place of his dim-witted 13-year old daughter, who
was not always able to follow his explanations with attention. On the other hand, I wasquite interested in his plans to render passable the hidden trails in the woods by cutting
off branches in the way. On such rambles through the woods he would always look forflowers and bring with him a beautiful bouquet for his wife. He had a wonderfully close
relationship with things that surrounded him in nature. He asked himself questions onplants, rocks, and clouds untiringly. Simply taking a stroll without observing wassomething he just could not do. Everyone accompanying him on these walks wasenriched by his eagerness to communicate. He was always particularly interested inclouds and in the flow in the various atmospheric layers. The beauty of some cumulus
clouds brought forth expressions of joy, and he spoke with equal enthusiasm about thechanging moods created when the landscape was illuminated in different ways by passing
cloud patches.
At night, when we children were finally in bed, my mother regularly read for my father
for almost an hour. He could not spare time for reading modern literature himself, but
liked to listen to it and did so with attention. This reading hour meant relaxation for him,and shutting off his mind from usual trains of thought. The books chosen by my motherwere mostly recently published biographies or novels, for instance Thomas Mann's Der
Zauberberg (The Magic Mountain). Once, listening to a reading of Erich Edwin
Dwinger's Die Armee hinter Stacheldraht (The Army Behind Barbed Wire), my father
was so greatly moved and distressed as he mentally reconstructed the experiences of acruel war scene, that my mother had to put the book down and stop reading. Oswald
Spengler's Untergang des Abendlandes (The Decline of the West) was another book soread, and provided occasion for many discussions.
When Mother died in 1940, Father had to go without this loved custom of being read to.
He missed it so badly, that I decided to cheer him up by reading to him for some time.
Later, he was content with listening to broadcasts on the radio at this evening hour.
After this reading hour, with no more demands made on him by anyone, he would sit at
the big table in the middle of the room, spread out his working papers, and passed hours
during which he worked away on his scientific problems. Light in the front room wasnever switched off before half past one. Neighbors knew the light in those windows, and96

I was told that people walked home feeling safe in the poorly lit street at that hour, since
Herr Professor was still awake and his light was burning.
In his working room there was another table at the wall which served for keeping mailstill to be dealt with and scientific journals. In time, the two piles would grow so high that
one was afraid of one or the other toppling over. My mother then pressed for clearing thepiles and helped at sorting them out. Although my father had chosen as his maxim theguideline: ''No postal correspondence can be so urgent, that, either it becomes even moreurgent by leaving them, or, it will be settled in the meantime of its own'', he was quite
willing to follow the suggestion of his orderly wife on Sunday morning. After that heliked to sit at the piano, and would happily 'prelude' away. Again and again, however, it
happened that he would search in the pile for some paper that had been laid there and hewanted urgently before starting out for the Institut in the morning, but in vain. Therefollowed repentance for time lost, and he would be very depressed by the failure of thesearch. Then my mother would join in searching---and although my father had spoken ofa blue covered exercise book, she found a yellow one with the right label and ask
humorously: "Is it perhaps this one?'' Her invaluable gift for picking out the right piecefrom those piles appeared amazing to me, and made her indispensable to her Ludwig insuch situations.

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14. Journeys on vacation
For all those years we went on journeys during almost all the holiday periods. During theEaster holidays, our destination was a spa in the Harz mountains, where we met with thefamily of Professor Otto Föppl from Braunschweig. My father arrived for the most part a
few days after us since he had a lot to attend to; but he used the single holiday week that
he allowed himself to go off hiking through the fragrant fir tree woods and enjoyed being
together with the two families. For the holidays at Pentecost we had arranged
accommodation in Sooden-Allendorf, and here too we met with the Braunschweig
family. There were also interesting subjects of conversation for my father during walks
with his brother-in-law. My father was not a demanding holiday guest. He was always
keen not to disturb anyone, and he returned the attention paid to him with kind words. He
never made use of his position, something which he could have done to turn any situation
to his advantage. On the contrary: it seemed to me that he placed other guests in aposition above his own. As a matter of course, he seemed to regard being considerate toothers and showing mutual respect as a natural form of behavior.
We spent most of the summer holidays in Föppl's old house on the Starnberg lake. The
name Ammerland sounded particularly pleasing to us in our ears. It was associated withthe delights of a carefree countryside life, and also with feelings of warmth aroused by
our feeling of being at one with our kith and kin in Munich.
The train journey to Munich took almost ten hours in those days, but the expectation ofreaching the destination we were longing to arrive at, made the journey pass by quickly. I
wish to put on record here an incident that occurred on one journey: we were traveling inan advance party with Mother since Father's university vacation always started 14 days
later, after our school vacation. A gentleman came into our compartment in Würzburgand started an animated conversation with my mother. On learning that we were from
Göttingen, he asked abruptly: ''Do you know a Professor Prandtl there?'' I have notforgotten my mother's spontaneous and hearty laughter at this question. We children
laughed too, out of astonishment, since we were quite unaware of how well known ourfather was.
My father very much liked the informal way of life in the Föppl-House. It was, becauseof this relaxed spirit, the most perfect place to spend the holidays: swimming in the clear
waters of the lake, hiking trips to the nearby mountains, and in between stimulating
discussions on scientific and technical matters with the brother-in-law and colleague,
Hans Thoma. On one trip - we had then climbed up through the garden- I remember arare natural phenomenon that my father was fascinated and excited about. Looking downfrom sunny heights over the fog layer, one discovered one's own shadow. The strange
thing was that we saw the head in each shadow surrounded by rays in the colors of therainbow. Of course he knew the physical explanation for this phenomenon, viz. that lightis refracted by the minute fog particles. But despite knowing the reason for it, he could
feel a natural delight on seeing the phenomenon.
In the summer of 1929 my father was to have a new honor bestowed upon him. At theGeneral Meeting of the German Society of Engineers VDI (Verein Deutscher Ingenieure)98

held on 22 June in Königsberg, a festive occasion attended by 800 engineers, theannouncement was made that Prandtl would be given the Grashof-Memorial-Medal, thehighest honor that the society can confer.
On 3 August 1929 Prandtl received the following letter:''In concurrence with the council of the German Engineering Society (VDI, Verein
Deutscher Ingenieure) I have the pleasure of inviting you and your wife to my villa on
the shores of lake Starnberger See on 10 August to present you with the Grashof-Medal.
With deep respects,
Oskar von Miller.''
Accordingly, on a nice summer morning on the 10th of August, several gentlemen from
Munich set out in a private motor-boot from Starnberg across to Ammerland. We picked
them up at the steam-boat foot-bridge and led them through the meadow paths to ourhouse. Herr Oskar von Miller, the founder of the Deutsche Museum in Munich, wasamong them. All the gentlemen were, as was made known, invited to his beautiful
country house in Niederpöcking. All of them went together, around noon, on board the
motor-boat in order to cross over comfortably to the other shore where the presentation
was to be held. In the evening of the 10th of August the honored guest was of course
brought back to Ammerland.
For my father, there was another special travel destination in Upper Bavaria that hevisited mostly in September when we children had returned to Göttingen with ourmother. The place was Schleching, close to Marquartstein. There, his two cousins, Klara
Prandtl and her sister Anna, had a quiet little inn. With these two he shared memories ofcommon experiences of childhood and youth, and he was always received there withwarm hospitality.
In the summer of 1930 we traveled once to Dahme on the Ostsee (Baltic See). The
International Mechanics Congress was to be held in August in Stockholm, to which, ofcourse, the wives were also invited. My parents wanted to shorten the long journey thereby traveling straight from Dahme to Sweden's capital. It is perhaps worthy of note that
the Föppl brothers and sisters all went there together: Professor Otto Föppl, Professor
Ludwig Föppl, Professor Hans Thoma and Professor Prandtl, husbands of the two sisters,
were all invited since all the members of the family held chairs in mechanics. However,at the large banquet the table was set for only one Professor Föppl at the long table, since
the prudent Swedish waitresses believed it to be an error of oversight that the original
name was listed twice. The result was that Ludwig Föppl, who had no seat at the table,
was requested to take a seat with the ''Festordnerinnen''. It so happened that through thisarrangement he met Christina, who was later to become his wife. Incidentally, withinsocial program's framework it must have been a wonderful family meeting in thischarming city in the north.

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In 1931 my mother went to the spa Bad Kissingen for medical treatment for healthreasons. His conscientiously written reports to his wife go to show the attention my father
paid in taking care of the minor domestic matters during this time: "Marie is looking after
us quite well. As a sign of my contentment I am sending her to the theatre tomorrow:''Land des Lächelns" (Land of Laughs). The children got their school reports today. For
the grades 1, 2, 3, 4 in the main subjects I have rewarded them with 40, 20, 0, -20
Pfennigs.''
During those weeks, at the request of his daughters, he also once took the time to cyclearound for an hour. When we were riding on our bicycles side by side along one of the
Göttingen roads, in the far distance and in the opposite direction, a car came along at amodest speed. Those days, cars made their appearance in the outskirts of the city only
rarely, so that cyclists and pedestrians did not feel any intrusion into their freedom. I
asserted: ''We two can keep cycling along side by side since we do not need more spacethan a car coming in the opposite direction.'' This drew a firm reply from my father: ''No,
we will now ride one behind the other; one should always make it as easy andcomfortable as possible for the other!'' This was one of his guiding principles in life that
determined his thoughts and deeds in his interactions with other people.
As a matter of course, in 1932, for my confirmation, he went to the evangelical church.
He wrote a few lines in my small bible that made me very happy. ''Remain true to yourkind! To fulfill one's duty in large matters as much as in small is the best way to makeone's soul cheerful and peaceful.''

100

101

small geneological table (or family tree) of the Prandtl family

The grandparents (Antonin Prandtl with his wife Anna Charlotte, nee Hauttmann)

102

103
The father: Alexander Prandtl

The mother: Magdalena Prandtl,
nee Ostermann

104
Ludwig: 4 years

6 years

105
10 years

12 years

106
17 years

20 years

107

L. Prandtl 1901,
Professor in Hannover

Prandtl at his self built water tunnel 1902

108
Gertrud Föppl with her
10-year younger sister
Else

1909 L. Prandtl, newly marriedPrandtl at the piano

signed sketch from his youth (following Nature)

109

The Friends, L. Prandtl and K. Schwarzschild with their wives,
both newly married

110

111

L. Prandtl with his first daughter
Hilde

Gertrud Prandtl with her daughters Hildeand HannaModellversuchsanstalt in Göttingen 1908

Die Aerodynamische Versuchsanstalt (AVA) 1918

112

113
Prandtl with his Institut -personnel

114
L. Prandtl 1924

With a model of the Flettner Rotor-Shipfrom left to right: J.Ackeret, L. Prandtl, A. Betz, R.
Seiferth115

Eleonore von Seebach at her
table in the Institut 1927

Mitarbeiter of KWI, from left Thirot, Görtler,
Oswatitsch, Dumitrescu,

L. Prandtl and A. Betz on their way to a lecture

The woman pilot Elly Beinhorn on a visit to Prandtl 1931

116

L. Prandtl with his daughter Hanna

In Fluid Flow Research Institut117

On the way to a university convocation

L. Prandtl and Prof. H. Blenk, 1938 in America

118

Prof. Ludwig Föppl, the brother-in-law, summer 1940 in Mittelberg

Geheimrat Max Planck, Prof. A. Sommerfeld and L. Prandtl in Berlin

119

120

Bundespräsident Th. Heuss,
L. Prandtl, W. Tollmien

Bundespräsident Th. Heuss, President of
the Federal Republic of Germany, in
Goettingenfrom left: A. Betz, O. Hahn, L. Prandtl,
K.F. Bonhoeffer (back), W. Heisenberg,
Bundespräsident Th. HeussSketch made by Gottfried Stein 1950

Lu Schang, nee Hsin Cheng, with her husband, and Johanna Vogel-Prandtl at Ludwig
Prandtl's grave12115. The year 1933
Now I come to the year 1933 and the time that we lived under the National-Socialists(NAZIs). As long as the Weimar Republic still existed my parents voted for the
Demokratische Partei which merged into the Staatspartei in 1930. However, they
engaged themselves very little with political issues and trusted the democratic
government of that time. This republic appeared to have proved itself, so that, in spite of
the economic crisis and the permanent quarrel between the parties, there appeared noneed to have serious doubts about its continuing to function.
In the house at Calsowstrase 15, in the floor above ours, when the window was open,
there was often a husky voice of a new election campaigner from the radio. We learned
that his name was Hitler and he had enthusiastic followers. My parents took scant noticeof it. They did not even nurture the thought of buying a radio then. When the downfall
came, it was unexpected for them. One could hardly understand how Hitler had
succeeded in taking over power. And thus began his twelve year reign as a dictator.
''The political corruptibility of the middle-class mind3 (Die politische Verführbarkeit desbürgerlichen Geistes)'' (H. Plessner) could soon be felt in Göttingen too. To a large
measure, a politically radical initiative originated from students who had subscribed in an
increasing number of members to the NAZI ideas even before 30 January 1933. Prandtl
had a composed attitude towards the political situation until then, since it had come byupon us without our involvement.
However, he was moved and enraged over ordinances that affected his colleagues.
In an article in the daily newspaper, Göttinger Tageblatt, of 7 August 1987, Dr. Marianne
Wiener-Bernstein remembers what some colleagues of her father, Professor Felix
Bernstein, who in 1933 had to emigrate, after he had been expelled from his Institut für
Statistik (Institute for Statistics), had said. I quote from the above-mentioned article:''I also know that Professor Ludwig Prandtl upbraided the Nazis aloud in his seminars.''
In the time that now followed, aeronautics research, in particular, received special
attention from the new government, an effect of which was that plans for erection of big
buildings on the Institut's site were realized. The considerably larger complex was headedby Prandtl as the first director. Generally, for a scientist engaged in research such adevelopment in general brings in much satisfaction. One may conjecture that Prandtl
would conduct himself in public as per the expectations of the day, viz. fall in line withthe political wishes of the supporters of the new projects, and i.e. align himself. But
Prandtl did nothing of this kind. In all those years, he stubbornly refused to become a3This book does not seem to be available in an english translation. A search showed Helmuth Plessner as
the author of the book with the following title in german which is available in libraries in U.K.: "Dieverspätete Nation: Über die politische Verführbarkeit bürgerlichen Geistes" published by Suhrkamp in
1974.

122

member of the Party or even allow a portrait (or picture) of Hitler to hang on the wall in
his Director's office. However, he was also never given the option, like so many others,of either subscribing as belonging to the Party, or to resign from his office. But I am sure,that in such an event, he would have given up his Director's position before giving up his
convictions to accept such a compromise. The majority of the young people in his Institut
also shared the same outlook.
But I remember an incident in these thirties when he came home for lunch very worried
and reported to my mother the following: He had walked home accompanied by an
Assistent, and this Assistent had told him on the way that he, availing the opportunity,
wished to now become a member of the Party. Prandtl found this attitude downrightenraging, but he composed himself and advised him, more in a fatherly tone, to refrainfrom that step. One should not subscribe to the ideas of the NAZIs, he should reflect on
the matter. The Assistent's reply that was repeated at our lunch table, which has engrained
itself in me word by word is: ''Herr Professor, wir wollen auch mal etwas werden, Siesind schon was! (Herr Professor, we too want to be someone (important) some day, youare already someone (important)!)''
Many conversations of these days, carried out in an excited state, have still kept me
conscious of the extent to which, in the year 1933, Prandtl was hurt by the baiting of his
Jewish colleagues. Much has already been published upon the development that started
with the Reich's laws and the passing of an ordinance sending German professors ofJewish origin on compulsory leave, to be later converted into an irrevocable dismissal.
For example, in the books by Alan D. Bayerchen [7], Scientists under Hitler,(Wissenschaftler unter Hitler), Constanze Reid [42], a biography of Richard Courant,
Max Born/James Franck: Luxus des Gewissens (Luxury of the Conscience, bookaccompanying the exhibition of Staatsbibliothek (Library of the State) Berlin, with text
contributions by F. Hund, H. Maier-Leibnitz and V. F. Weisskopf [47]). (to check title oftranslations of these books) Here I will restrict myself only to those in which there is areference to Prandtl.
From the publication ''Luxus des Gewissens (Luxury of the Conscience)'':''James Franck, who served in the First World War in the combat troops, was notdismissed from the office he held in his teaching post. But his pride and solidarity with
his Jewish colleagues made him take a path of his own. On 17 April 1933 he resigned.''Prandtl was deeply hurt and sad. Even as late as 10 February 1933, together with othercolleagues, he had signed a letter to Franck who had received a 'call' to Berlin, with theobject of keeping him in Göttingen.
''The significance and performance capability of our faculty rests upon personalities
working together as a group. In the last few years the group has already suffered heavy
losses with far reaching consequences. Your departure would leave the edifice that has
been built here with your assistance, exposed to decay in particularly difficult anddangerous times.''123Signed: Hilbert, Born, Windaus, Prandtl, Reich, Pohl, Neugebauer, Courant, Schermer,
Eucken, Kienle, Angenheister and a few others. 4
The biography of the Jewish colleague Courant contains a detailed and accurate accountof the course of events in the University as far as Courant himself is concerned. The
chapter '' Spring 1933 '' presents an account of how much Prandtl stood up to help thecolleague in distress about whom rumors were spread that he is a communist agitator. I
wish to quote a few passages from this book. 5'Although he had not received official notice of his status, he made up his mind to
approach officialdom.
Seeking a colleague unaffected by the Reichsgesetze who could present his version of his
activities to the administration of the university, he chose Prandtl. The professor ofmechanics was generally considered a somewhat naive person. But during the hectic
week following the announcement in the paper, he had acted with courage and decision,
dismissing one of his Assistents when he had discovered him to be a spy for the NAZI
powers at the university. 'This person is said to have tried to ward off his dismissal and someone remembers thewords uttered at the time of his taking leave: ''Herr Professor, you will repent it, you will
think of me!'' I wish to include here that it is hard for anyone to understand today what it
meant at that time to dismiss relentlessly from his post someone in the favor of the rulingparty ruling and who was supposed to render services as a police spy to his superiors.
One should keep in mind that, on the top of everything, Prandtl, by his very nature, was
not inclined towards radical solutions.
Now back to our text on Courant where it goes on: ''It (both Prandtl and Courant) decided
that Courant should write a letter to Prandtl setting out the facts of his political activities
after the First World War. Prandtl would then present the letter to the Kurator (trustee). ''I wish to quote one more passage from the Courant-Biography. It concerns the drafting ofa petition in his support, conceived by Courant's colleagues, Friedrichs and Neugebauer,
which was to be sent to 65 colleagues. It was a declaration on the reputation Courant had
achieved on taking over the Mathematische Institut as successor from Klein. The author(Constance Reid) writes 6''… sixteen replied not at all…, twenty-one refused to (put their signatures) sign but wrote
letters explaining their reasons.

4

In 1953, the year in which the city of Göttingen celebrated its 1000 years of existence, Franck, Born and
Courant were honoured by granting them honorary citizenship of the city of Göttingen.
5
Author quotes from the German translation, here verbatim from the English original Constance Reid:
Courant, Springer-Verlag, New York, 1976, p. 145
6Author quotes from the German translation, here verbatim from the English original Constance Reid:
Courant, Springer-Verlag, New York, 1976, p. 150.

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There were various reasons…There was an admitted feeling on their part that, much as
they would like to support Courant, they did not want to bring themselves as individuals
to the attention of the government. He was ashamed, the writer concluded, but he had toadmit that he dreaded the consequences if he signed. ''With this response, Professor Kneser, a former Assistent to Courant, considered it to be
more effective to draft a letter that would reach the minister straight. 7''… The suggested letter, which was signed by Friedrichs, Kneser and Prandtl began (asfollows):'Each of the undersigned knows Professor Courant as the result of a number of years ofclose collaboration. To our knowledge in all of his activities he has felt himself a German
citizen and a representative of German science, and has conducted himself as such…The
mathematical facilities of Göttingen, which since 1921 have been developed essentiallythrough his efforts, are of great significance for the scientific culture of Germany and will
not without essential damage be separated from his person.
The letter concluded with a request that the three signatories be heard in person (and, if
this was not possible, that they be permitted to contribute their testimony regarding
Courant in writing)."
At the end of two weeks, the petition drafted by Friedrichs and Neugebauer was signedby 28 colleagues, some of whom were: Heisenberg, Hilbert, von Laue, Planck, Prandtl.
These text passages that I have taken from Courant's biography, appear important to me
to prove the extent to which Prandtl exposed himself without fear of possible
repurcussions.
There is a paragraph in Article 4 of the civil-service laws which reads: ''Civil servants
whose political involvement raises doubts upon their unequivocal commitment to thenational State can be removed from service. Standards of judgement for civil servants inmanagerial positions of responsibility are to be applied on a stricter scale.''It is also interesting that these efforts for Courant's rehabilitation were actually fruitful.
The suspension order was cancelled. Later, Courant took retirement as an Emeritus andfinally, with a heavy heart, migrated to America, but with a financially somewhat morefavourable condition.
The grip of the rulers did not spare any of the Jewish Dozents of the university. Yet
Prandtl did his most to counteract the injustice. There were more suspensions. On 16
September 1933, Prandtl wrote to his wife from Würzburg: ''The Kurator writes to me

7

Author quotes from the German translation, here verbatim from the English original
Constance Reid: Courant, Springer-Verlag, New York, 1976, p. 151.
125

that the Minister has withdrawn Hohenemser's Venia Legendi. Things have thus come so
far!'' Prandtl had pleaded in support even for him and had tried to prevent his dismissal.
As a consequence of intrigues by another agitator in the Institut, some other colleagues
were also charged since they had interfered in the affair through their statements. The
awkward differences and accusations were reported as per rules to the KWG (KaiserWilhelm Gesellschaft)-Administration and their opinion was awaited. The response that
followed was a circular from the President of KWG: In order to re-establish an
atmosphere of tranquility at work, the seven employees who had given statements as
witnesses were to be dismissed. This was not in tune with Prandtl's line of thought.
The complications of the case in which the name of the Georgian Dr. Nikuradse
repeatedly crops up, have never been cleared up entirely. Persons of different ranks
endeavoured for a prosecution of the matter. I quote from the files of the lawyer tofacilitate understanding of the situation that had now arisen: ''After Herr Professor Prandtl
had refused to follow the orders for dismissal, there took place on 29 September 1933 ameeting with Herr Geheimrat Valentiner, Geheimrat Wolff and SS-Hauptmann
D.J.Weniger, who came in suddenly, and at which Weniger explained to Professor
Prandtl that it is now immaterial whether there has been a misjudgement or otherwise, thedecision to dismiss the seven men has been taken, and it should becarried out
unconditionally. Herr Professor Prandtl was merely the executing organ. Should herefuse, he puts himself at the head of a revolt against the national State and must reckon
with being sent to a concentration camp.''In spite of this serious threat Prandtl did not give up supporting his Mitarbeiter andmaking known to the Prussian Ministry of Education the truth regarding the events---on 4
October he had requested for a conference in person in Berlin----to fight for reinstating
the innocent.
The conflict of opinions continued to swell.
28 December 1933, Prandtl to Planck:''I should not also conceal that, through the treatment meted out to me in the new letter, inwhich my representations are rejected without reason, I would feel hurt in my honour as
the Director of a Kaiser-Wilhelm-Institut. The reason: My conceptual understanding of
my duties and responsibilities towards my Institut goes much deeper than merely
standing to attention to the superior authorities and executing an order of theirs that I
regard harmful to the Institut, without exhausting the last possibility of coming to anagreement.
29 December 1933, Planck to Prandtl:''Would you not want to let the matter rest at last? Basically, the three men (in themeantime four had left of their own accord) will come through the terror shaken with ajolt, and for the rest they will stay for their scientific work which gives them the best126

opportunity to wipe out the blot. What hurts me most in all this is the thought that you
yourself believe you must invest your precious time and effort in this obnoxious matter
into which you have been drawn by fault of others. May the New Year bring better days
for you and your Institut.
With warm greetings from house to housealways devotedly yours, Planck.''
3 January 1934, Prandtl to Planck:''The reason for my not letting the matter rest, as you suggest, is simply as follows: I wish
to keep faith with my people who have entrusted into my hands the defence of theiraffairs. And I myself have the liveliest interest in correcting the picture of conditions in
our Institut that has arisen from the discussions.''
Let the reader form an impression himself from these quotations from letters on how
Prandtl conducted himself in a straightforward and incorruptibly firm manner following
his own convictions. In the end, thanks to Prandtl taking a firm stand on their side, thethree employees could retain their jobs that were legally theirs.
During the course of these unpleasant discussions, one was surprised to come to knowthat since several years Nikuradse, as a NAZI activist, had cultivated confidential contacts
with the Party office. ''In order to re-establish an atmosphere of tranquility at work andfunctional capability of the Institut, Prandtl dismissed him (Nikuradse) although by thismeasure he drew the enmity of the SS-Hauptmann Weniger. The attempts of the SS-secretservice-man to do harm to the Professor however went without success. In spite of theiritationthat the case of Dr. Nikuradse had brought to the Head of the Institut, Prandtl saw
to it that he (Dr. Nikuradse) got an equivalent job at the Breslau University.
His conduct was similar in March 1934. Regarding the other case involving a person, I
will quote from the account presented by Kurt Kraemer in his ''Institutsgeschichte(History of the Institut)'' [17]:''In March 1934, the law for re-establishing the officialdom of professional civil service(that had already served as a reason for dismissal of Jews at the university) had to be
applied at the KWI (Kaiser Wilhelm Institut) for Fluid Flow Research too as follows: On
10 March (confidential), the Director-General of KWG (Kaiser-Wilhelm Gesellschaft),
Glum, asked for declarations of loyalty from those institute personnel who were Social
Democrats earlier, and demanded dismissal of one supposed to be a communist. Prandtl
replied on 13 March’… I may be removed from the directorship of the local institute if
the opinion is held that I am no longer suitable to hold the position, but I cannot be asked
to dismiss a precious skilled worker only because once as a young man he got attached
for some time to a youth organisation that stood close to communist ideas.' On thegeneral administration checking up with the Reich's Ministry of the Interior, it turned outthat as a matter of principle no exception can be made, except when . . .

127

On this President Planck himself wrote on 10 April (confidentially!), that the coppersmithin question may continue being employed if Prandtl personally shoulders the complete
responsibility and no complaints are raised by the leader of the NSBO (the cell in theinstitute). This is how it turned out to be.''Prandtl did live mostly in the abstract thought world of his research, yet he was always
ready to take time to listen to the plights of his fellowmen and Mitarbeiter, attend to theirneeds and offer effective help.
In his work [46] which he has titled ''Das geistige Erbe Ludwig Prandtls (The inheritanceof Prandtl's spirit)'', Professor Schulz-Grunow writes:''Prandtl's readiness to help should
also not be forgotten. He literally took care of the life and well-being of his Mitarbeiter.
During the economic crisis of the thirties he renounced his pay as the Institut's Director infavour of needy Mitarbeiter, and, when the war broke out, all of us were released.''
There existed a totally personal relationship between Max Planck and Ludwig Prandtl.
His (Planck's) second wife was my mother's friend at school in Munich (she became mygod-mother), and the two companions in youth stayed in close touch with each other evenafter their marriages.
Even in private circles with Max Planck, one was impressed by his ethics of strict
fulfilment of duties. It might be seen as very fortunate that this distinguished person of
integrity who was an example to follow in every respect, was responsible for holding theoffice of the president of KWG during the first years of the totalitarian regime.
The tasks in the realm of Prandtl's Institut were growing. The more the leading men oftechnology thought along the lines of the aerodynamicist, the more did the area of work
expand. When, in the summer of 1933, the 25th anniversary of the Aerodynamische
Versuchsanstalt (AVA) was celebrated, a large number of renowned scholars andindustrialists had gathered together in Göttingen. During a round tour visit of the halls of
the Institut one could see and admire many different models: Besides the aeroplanemodels there were models of streamlined cars, fast rail-cars and models of transmission
towers on which the wind pressure had been measured. The public also participatedactively in the new research.
The generosity of the city of Göttingen was very welcome. On the occasion of the jubilee
celebrations it had donated a piece of land at the airfield for erecting a special flighthangar for purposes of the AVA. The state secretary of the Ministry for Aeronautics had
likewise chosen the time slot of these celebrations to announce in person the granting of
permission of a new construction phase. A more modern, larger wind-tunnel that wasurgently needed for research purposes was to be built on the land at the Bunsenstrasse. A
year later, in 1934, construction was started spectacularly by the ground-breaking
ceremony; and following a two year construction activity, the new wind-tunnel could becommissioned in 1936.

128

129

16. Honorary doctorates from Cambridge and Trondheim
In early July 1934, Prandtl traveled with his elder daughter to Cambridge to participate ina meeting of the Congress for Technical Mechanics8. He was a guest of his English
colleague Prof. G.I. Taylor and gave a lecture at the Congress [20].
In 1936 he was invited again to Cambridge where the degree of honorary doctorate wasto be conferred upon him.
9 June 1936, Cambridge:''Just now I have the first free hour after I gave my talk yesterday. It went off well. The
days with the Taylors were very relaxed, filled with conversations of all kinds. In anothertwo hours the ceremony starts. I am glad I do not have to say anything since my voice isvery hoarse today.''
10 June '36:''It was very festive yesterday. Lord Baldwin, the Prime Minister, is the Chancellor of the
University and performed the ceremony (of awarding me the honorary doctorate). I willtell you in more detail later. Tomorrow I am in Farnborough, and in the evening in
Berlin.''A note in the newspaper ''Berliner Lokalanzeiger'' on 3 July 1936:''An English honorary doctorate for Ludwig Prandtl. Cambridge University has awarded
an honorary doctorate to the President of the Society of Applied Mathematics andMechanics (GAMM- Gesellschaft für angewandte Mathematik und Mechanik).''Prandtl had been invited to come to Trondheim in Norway on 15 September 1935 toreceive an honorary doctorate from the Technische Hochschule here. The decision toaward him an honorary doctorate had been taken a year earlier, but he could not bepresent in person on the festive occasion then. The scroll, and the ring that came with
together with the document, were therefore sent to him. It was only two years later, in
September 1937, that Prandtl could meet the Norwegian colleagues in Trondheim; hedelivered a lecture to express his thanks for the honorary doctorate. He was then invitedto Oslo also.
The friendship with the Trondheim colleagues was very sincere. In the post-war years of
acute shortage (in Germany), Professor Brün from Trondheim sent us several bottles ofvaluable fresh cod-liver oil through a private courier, although during the period ofOccupation he had himself stood against the Germans and worked for the underground.

8

Translator's note: This must have been the Fourth International Congress of Applied Mechanics, held in
Cambridge, England13017. The house in the mountains
At this juncture I wish to write about an event still from the year 1935. It is of a more
personal nature that came by mostly due to the initiative of my mother. My parentsbought a site in Kleines Walsertal (name translated: Small Wals Valley) in Austria, andgot a modest wooden house (chalet!?) built on the same. They had always refused tomove towards possessing a house of their own in Göttingen, in contrast to what most of
their colleagues in the thirties did. For them it was more attractive to have a small
property of their own in the south German area. We knew the place Mittelberg for someyears. In one of the homes for children there, my sister had spent some time of repose.
Later, we had been several times to this high altitude valley for our winter holidays. From
the diary of my mother:''In the year 1934, when we spent Christmas again in the House Schaule in Mittelberg andLudwig reconvalesced there so well from a severe attack of cold, the wish was born inme to buy a small house of our own in this beautiful and healthy spot on earth. In Easter
1935, I already conducted negotiations on the site and construction of the house, whichslowly sprouted out of the earth in the summer.''
My father drew up the plans for the house himself, according to which the work wasdone. In December 1935 already we spent our first winter holiday in this cottage. From
the diary:''During the first few days there was not much of coziness when the heating system did
not function properly. Later, the house owner was sufficiently experienced to give up thisexpectation. He liked looking after his house and once said, it is a wonderful toy. Manytimes during the day he was seen going around with a saw and hammer to put things inorder.''
They had meant to move in there into that house after retirement, and had nurtured plans
for the same. But things took an entirely different course.
Friends and relatives visited us in the remote valley, and shared with us the joy of skiing
and mountaineering. The clear and delicious mountain air refreshed young and old, andthe informal evenings with games, chat and gossip, and useful occupations, mostly withthe warm-hearted host, have remained in the pleasant memory of everyone.
It could happen that, when my mother held knitting material in her hands with the yarn ina mess, my father observed her pulling it up impatiently. It had got into a hopeless tangle.
He looked up from the letter he was writing, saw for awhile, and then said: ''Let me try
once to put it in order.'' However my mother found that he could spare himself thattrouble. But he didn't let go from what he had undertaken to do and merely told: ''It is fun
doing it!'' The difficulty in solving a problem had an irresistible attraction for him. He
wound the wool, put it through and untied the knots with care, and everyone followed his
manipulations attentively. He applied himself to this simple occupation with patience and131quiet eagerness, and one was thoroughly entertained as an onlooker. One watchedintently success coming in gradually that he finally brought to an end as in a game.
I wish to supplement my description by a passage from a letter written much later.
Prandtl wrote on 17 April 1952 to Professor Marguerre from whom he had obviously
received a book: ''The packing of the book, it appears to me, is your own work. I found it
noteworthy that the knot, that was indeed tied securely, could be undone to recover the
single thread undamaged. This is a kind of game for me (it could also be said it is a gameof patience). The solution turned out to be unique without searching, and the thread was
put away in store for further use.''I wish to mention an incident that has remained in unforgettable memory of a young
cousin of mine. Visit on holidays! The beds for the several guests were arranged in such a
way that my father shared a room with his nephew. At four o'clock in the night mynephew was woken up gently by him (my father). My father asked him to get up and took
him to the open window. There he showed him a star that shone standing out brightly inthe sky above the mountains, and explained to him that it is Venus, a planet of the solar
system. In this quiet night, both enjoyed the beauty of the clear starry sky and wereabsorbed in meditative watching at the sight of the morning star sending across its
greetings with twinkling light.
A friend of ours also remembers even in her advanced age a noteworthy saying ofPrandtl. In those days in Mittelberg, when she accompanied him on a walk, they saw at
the edge of the meadow a grasshopper taking its tender jumps. ''Something like thisoriginal small creature the human being can never reproduce in spite of permanent
technical progress. It is a marvel of creation.''Of the many visitors who stayed in that cottage in those years, there is one family ofwhich I wish to make at least a mention. In the autumn of 1936 my parents placed their
new vacation domicile at the disposal of a friend and colleague, the philosopher Georg
Misch, for whom the commission to teach at the Göttingen University had been
withdrawn due to the ''Arier''-Clause. They had also been given notice to leave thehousing, so they were glad to accept my father's offer. Austria had not yet become part ofNazi-Germany by the ''Anschluss'', so there was no cause to fear investigations there.
Misch's grown-up children were forced to leave Germany, and before they migrated into
a foreign country they visited their parents once again there.
Their son Peter had accepted a professorship in Canton (China). He wrote in our guestalbum: ''19 September 1936: Just before departure to Canton for the last time in ourGerman mountains, to take leave of parents who, it is comforting to know, are well takencare of in the cosy Prandtl-House. It was nice to be together for the last few days.'' Theirdaughter Lore (later wife of the Nobel-Prize winner Felix Bloch), who came from
Denmark, traveled over Mittelberg to Switzerland; the youngest daughter, my friend Lilli,
traveled from there to England. Later all the three children, brother and sisters, lived in
America.

132

Professor Misch wrote in our guest-album on 7 March:
September, October, November
and almost the whole of December,then again in the new year
until beyond the end of Februar'.
Thus we lived for 6 months
in Prandtl's house on the mountain slope,
two together in solitude;
the mountains rise over happiness and misery.
Some come and knock,whether one can live here?
Yes, comfortably! But not everyone.
The lady of the house, she has the say!
She let it for friends for a long time,
she is indeed always ready to do good.'' 9
Misch left Germany at the end of 1937 and went to England, whereas his wife, daughterof Wilhelm Dilthey, stayed back in Göttingen due to her delicate health. Her husband
rejoined her in Göttingen after seven years of separation in May 1945.
Extract from the ''Universitätszeitung'' no. 2 of the year 1946:''On the return of the Göttingen philosopher from emigration: With the return of Georg
Misch, one of the most significant personalities of German philosophy has come back toGöttingen from emigration. We have every reason to be grateful to him for having taken
up his earlier teaching position again.''
In February 1938, my sister Hilde got engaged with the legal intern (Gerichtsreferendar)
Wolfgang Weber. The head of the family, Rudolph Weber, was a critical person of highcharacter, who had relinquished service as a minister in Oldenburg since he was
9German original:

September, Oktober, November
und fast den ganzen Dezember,dann wiederum im neuen Jahr
bis über Ende Februar.
So lebten wir 6 Monat langin Prandtls Haus am Bergeshang,selbander in der Einsamkeit;
die Berge ragen über Freud und Leid.
Und manche kommen und klopfen an,
ob man denn hier nicht wohnen kann?
Jawohl mit behagen! Doch nicht jedermann.
Die Herrin des Hauses, auf die kommt es an!
Sie ließ es Freunden so lange Zeit,
ist sie doch stets zum Guttun bereit."

133unwilling to enter into any compromise with the NAZI-government. Wolfgang's sister,Dr. Sophie Weber, was a pediatrician, later the trusted doctor of my children who stoodby the side of all of us for advice. Destiny however took away from the bride thishappiness, bringing in sorrow for all of us. On 16 September 1939, the war-time wedding
ceremony had taken place in our home, and soon thereafter followed, with the calling of
the young husband for service, the agonies of separation. On 29 June 1941 Wolfgang
Weber fell as lieutenant still before reaching Riga.

13418. Pleading for W. Heisenberg
For a long time, there had been a burning controversy in physics between adherents of aso-called ''arisch physics''---supported by Alfred Rosenberg---and those of modern
physics. The representatives of the first group, who stood against quantum theory andEinstein's theory of relativity, demanded that physics should have a more ''pragmaticcharacter''. Since, over and above this, these experimental physicists (Johannes Stark andPhilipp Lenard belonged to this group) regarded themselves as a political movement, they
tried to rule over the entire community of physicists in Nazi-Germany through intrigue.
In 1937 they directed massive attacks against Werner Heisenberg, then a young professorof theoretical physics.
Following these attacks, many colleagues of Heisenberg who held him in high esteem
rallied together and dared to take the risk of defending him through written protests sent
to the ministry. Even Heisenberg's own action - he wrote a letter himself ''to reestablish
his honour'', which he sent to the SS- Reichsführer Heinrich Himmler - had not borne
fruit. A thorough and detailed account of this incident which stretched over a year, is in
the (German) book with the title ''Erinnerungen an Werner Heisenberg'' (Memories ofWerner Heisenberg) authored by Elisabeth Heisenberg [12]. Here it suffices to note that
Prandtl also stood up openly on the side of Heisenberg in this dangerous affair, defending
him vehemently against the charges made. Thus, Prandtl helped Heisenberg greatly in theprocess of rehabilitation.
In his book ''Scientists under Hitler'' [7], the author Alan D. Beyerchen, who deals
extensively with ''the Heisenberg affair'' and its complete history, writes about the way inwhich Prandtl tried to help his young colleague get out of this situation:''The case of Heisenberg remained unresolved until the peak of the summer (1938). In
July there came in important support from Ludwig Prandtl, the Göttingen specialist in
aerodynamics, who was seated next to Himmler at a gala-dinner organized already sometime ago by the German Academy of Aeronautical Research (Deutsche Akademie für
Luftfahrtforschung). Prandtl had waited until he thought the SS-Führer was free fromurgent commitments arising out of annexation of Austria in order to get a hearing for his
defense of Heisenberg.''
On 12 July 1938, Prandtl reminded Himmler of their talks in a letter. ''When I was seatednext to you on the occasion of the festive meeting of the German Academy of
Aeronautical Research on 1st March of this year, I brought up the matter of certain
difficulties faced by Germans in the field 'Theoretical Physics' due to the unjustified
attacks made by a group of experimental physicists, and mentioned in particular the
personal difficulties of Herr Heisenberg. I wish to add a few words to what I said then on
theoretical physics. The difficulties people in this subject are put into are primarily
caused by a small group of experimental physicists, who have not been able to keep pacewith the research work of the theoreticians, vehemently opposing the new developmentsin theoretical physics, primarily on grounds that there are significant elements in thefoundational structure of physics today that come from 'non-arisch' scientists.

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''But there are indeed, among the 'non-arisch' people, scientists of a class that must be
regarded as the foremost of the best. I wish to recall of the short-lived Heinrich Hertz,
who proved the existence of electrical waves through arduous and imaginative
experiments - the same waves that have risen high in technical importance due toapplications in wireless telegraphy and radio. The physicist Einstein belongs to first classphysicists through and through.
''Science simply faces the fact that laws have been discovered that in turn have led tofurther discoveries which cannot be ignored without dismantling the structure on which
they were built. Next to theoretical physicists, there will always be experimental
physicists whose strength lies in conducting experiments for which they will get thetheory worked out by the theoreticians. But it is unheard of when such experimentallyoriented people, because they are unable to follow the theories, simply declare them to bepernicious and reprehensible, and indulge in mud-slinging at those representing theory. In
order to draw your attention to the opinion of the well-known theoretical physicist Max
Planck, I wish to enclose extracts from a talk by this scholar.
''Regarding the person of Herr Heisenberg, he has indeed been grossly insulted by Stark.
It is urgently necessary that the abuse is retracted, and it be made clear that officials at theGovernment as well as the Party leadership do not share Herr Stark's views. This isabsolutely essential, since letting this slander go without a rebuttal would make it very
difficult for Herr Heisenberg to be effective as an academic teacher; for the reason thatthe students would be taught that what they can learn from him is useless -indeed
harmful---and detrimental to the development of their technical expertise,''I think an appropriate measure would, if possible, be to let Herr Heisenberg publish an
article on a subject of his choice in the journal 'Zeitschrift für die gesamte
Naturwissenschaft ' which appears as an organ of the science section (Reichsfachgruppe
Naturwissenschaft) of the Reich's Student Leadership (Reichsstudentenführung). I would
be glad to get in touch with Herr Heisenberg regarding the choice of a suitable subject.''
I will quote Alan Beyerchen again: ''There is hardly any doubt that Prandtl's vehemently
worded defense of Heisenberg and of theoretical physics played a decisive role in thematter. Hardly two weeks later, Himmler wrote to Heydrich saying that he concurs with
Prandtl's letter and is of the opinion that the Students' Association should allow
Heisenberg to publish in its journal.''However, the professor's chair for physics in Munich that had been already earmarked in1935 to go from Sommerfeld to Heisenberg, went instead to a physicist by name Wilhelm
Müller. Again, Prandtl did not mince matters while expressing his opinion: ''Herr Müller
does not possess any qualification whatsoever for theoretical physics. Instead, he has
published a polemically worded program of work that can only be described as an act ofsabotage of a subject that is indispensable for further technological development.''(Memorandum of May 1941, quoted in E. Heisenberg [12])13619. Voices on the situation at that time
At this point the younger reader may find no way of getting away from the question: How
could Prandtl approach Himmler, who should be held responsible for some of the mosthorrid crimes of the Nazi regime? That question can be asked only in a state of ignoranceof the situation at that time. Most certainly, the words of the historian Christian Maier,
who points at the trustfulness and unsuspecting nature of the Germans, would bear moreweight than any answer I could give. A lecture given by him in Tel Aviv, with its criticalanalysis, aids in understanding these problems. I quote from this lecture Verurteilen und
Verstehen (Condemning and Understanding), (Frankfurter Allgemeine Zeitung of 28
June 1986).
''They (i.e. a section of Germans) could indeed make out from the start the wrongdoingsof the National-Socialist-regime, but could not already know on this account the gigantic
proportions to which their country had set out to commit a crime of a unique nature. Had
holocaust been forecast to them, they would not have believed it to be possible, and that
not only because they had been brought up mostly in an atmosphere of politicalunawareness and extraordinary respect for the state. When does it happen that a wholegeneration is asked a posteriori that it should not have made use of the chances in theirprofession since that would necessarily bring them in close contact with those holding
power? What would we of today have done in such a position? Only if we knew that wewould have done better under conditions prevalent then and with the state of knowledgeof those days, can we condemn Germans of those days, with the exception of those who
committed offences and crimes. . . . We have every reason to resolve to do better;
especially since we can know today what a totalitarian regime is and how it originates.
But there is no justification for us in a much more fortunate position to put on a
Pharisaical attitude.''At this juncture I wish to add one more incident from memory - a conversation from theyear 1943. My father had returned from a walk that he had taken in the company of agood friend, He said: ''Do you know what Frau X told me? In the East, Jews are being
herded together and killed! How can one believe such nonsense! During the last war, theFrench also spread such tales, that the Germans committed atrocities on women andchildren.'' It was in his very nature that he was not in a position to imagine such things
were possible, or even that they could be thought.

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20. Congress in America
On 1 September 1938, Prandtl started on a trip to America in order to participate in the''5th International Congress of Applied Mechanics'' in Cambridge, Massachusetts. He wasalready 63 years old then. He traveled together with Professor Blenk, Dr. SchultzGrunow, Professor Schlichting and many other congress participants. They met together
on board the steamship ''Bremen'' for crossing the Atlantic. My mother utilized theabsence of her husband for a renewed period of stay in a sanatorium in Kissingen which
was urgently recommended to her by the doctor. There, she got the following letters fromher husband:7 September 1938:''The journey has gone on smoothly and even lively up to now. The ship is very beautiful,the meals royal, our company very pleasant. Every morning I take a ride on a camel and ahorse (both living on the principle of an electric motor) and then swim. The weather hasoften been very nice. Now and then the day is also foggy, and there is a little stiff windon the Gulf Stream. We are supposed to be in New York at two o'clock in the morning
tomorrow. From the landing piers we will be brought to the hotel, and do not have toworry about anything for twelve days. 130 lectures are supposed to be given at thecongress, three simultaneously (in parallel sessions). But even 43 is still too many. . . ''After arriving in Cambridge, Prandtl met, among colleagues from foreign countries, old
acquaintances as well, like Professor von Karman, Professor G.I. Taylor, with whomsome personal thoughts were exchanged. In his biography [15] von Karman tells his coauthor Lee Edson on the conversations in 1938. He (Lee Edson), however, published thebook on his own only after Karman's death. In this, certainly, not sufficient care wastaken in differentiating between what was really said, and what Karman interpreted withhindsight.
In professional circles that have come to know of Karman's book ''The wind andBeyond'', the view is held that this biography should be read critically. In a meeting of therecipients of the Ludwig-Prandtl Ring on 9 May 1972,10 Professor Blenk expressed hisview as follows: ''The Autobiography of Karman cannot make any claims of historicalcorrectness, which should be kept in mind by every reader of this otherwise interesting
book.''
Prandtl, who had been sought by the ministry in Berlin to recommend a venue for the
congress to be in Germany, had agreed to place before the foreign colleagues aninvitation from the German government. Through this he had hoped to continue
cultivating scientific exchange with the other countries in peaceful coexistence. The
invitation triggered excited political discussions between the colleagues from thedifferent countries in Cambridge, which has remained in the memory of the participantsin the congress who are still living.

10

Translator was present at this meeting.

138

Professor Blenk wrote Dr. Rotta on 9 July 1987: ''I remember well the tense, in part quite
unfriendly atmosphere at the congress that was prevalent between the German and theother participants. There were many small discussions on the necessity or the likelihoodof the second World War, at which we Germans did not mostly see its necessity. In these
discussions we defended the policies, not the ideology or the crimes of Hitler, insofar as
they were known at that time at all. What we believed we were right to defend were: 1.
abolishment of the Versailles proclamation, 2. reinstatement of the right to arm, 3. theunion with Austria to form a ''Grossdeutscher Reich''. It is interesting to read what ahistorian like Sebastian Haffner writes on these themes in his book ''Anmerkungen zu
Hitler'' (''Notes on Hitler'').
Prandtl also had attempted in discussions with the foreign colleagues to defend his
country against derogatory judgments of current Germany. At that time he believed,
without being at least critical, in the good intentions and straightforwardness of his
government.
Men, who like Prandtl, had grown up in Kaiser's Germany, and in whose thinking loyalty
towards the powers that be and patriotism were closely knit with each another, felt it as
their duty, particularly in interactions with foreigners, to justify the political events athome through defending their country against slander. This attitude is visible in his
foreign correspondence too. Soon after taking leave of the German group, G.I. Taylor
wrote in retrospect upon these talks:
27 September 1938 (three days before the Sudetenland crisis):''Now I must ask you to believe that, whatever happens between our countries, thefriendship and admiration which I, in common with aerodynamical people in all othercountries, feel for you, will be unchanged. I realized that you know nothing of what thecriminal lunatic, who rules your country, has been doing, and you will not be able tounderstand the hatred of Germany which has been growing for some years in every
nation, which has a free press.''
Later, Prandtl had of course to see his political mistakes that Taylor was referring to here.
After the congress closed, there was on the program for the participants a visit to theWorld Exhibition which was in the process of being put up at that time.
During the Atlantic crossing that the German scientists' group had undertaken aboard theAmerican liner ''New York'', the news came in of the occupation of Sudetenland by Hitlerthat was to come. This made the ship's captain take a detour in order to avoid getting into
a possible war-zone. The ship headed towards the Norwegian coast; but since the crisis
had been overcome in the meantime through the Munich agreement and the situation had
calmed down, the passengers on the ship could be landed on German soil, although withsome delay.

139

It appeared now that the judgment of the German government having peaceful intentions
was confirmed, and that predictions of the bad had rightly been refuted. In his reply to
Taylor, Prandtl indicated that he had not given up his earlier standpoint to defend theGerman position as it stood. His reasoning, however, remained not understandable.
Prandtl, who, as said earlier, trusted the news appearing in the papers, could not imagine
that already one year later it would be a state of war.
When after all this, war broke out on 1 September 1939 with the attack on Poland, myfather had painful thoughts, after all this generation did know enough of the miseries ofwar. ''Work will go on as up to now'', that was his laconic directive to the personnel.
The first winter of the war saw the people in Göttingen having to put up with some
restrictions. In February 1940, families in ''Saarland'' were evacuated as a measure toprotect them from the fighting in the war with France. The occupants of the more
spacious floors in our building were asked to house some refugees, around two or three inevery floor. The family of a mine-worker with its seven members came in to the house
where we were living, and they were accommodated by three tenants. My mother was
full of sympathy and kept our spacious kitchen at their disposal for the evening gettogether by the family. My father also took time to go there to speak with them a little
longer now and then. Some other apartment owners moaned over the burden of having tohouse another. The people from Saarland stayed for around three months in their quarters
before they could return to their home villages.
Our family was hit by several severe blows of destiny in the years 1940 and 1941. At theend of July, my sister lost her baby soon after birth. In December, my mother died. I havealready referred to the death of my brother-in-law who fell in the war close to Riga.
These were difficult times for all of us. Since her marriage, my sister was not living with
our parents, so, after my mother's death only my father and I were left in the bigapartment. My father missed the care and refreshing liveliness of my mother with which
she was participating in everything. It was often very quiet in our place. I continued mystudies of language and literature and concentrated, with the best I could, upon thelectures. The housekeeping work ran well and smoothly, thanks to a reliable maid.
Regarding the rest, I tried to adjust myself to Father's habits so that he should not missanything in day-to-day life.
As usual, my father took a longer walk every week-end at which I accompanied him.
During the Easter holidays of 1941 we traveled together to visit our South German
relatives in Munich and his cousins in Schleching. With the help of these lovable people
we finally succeeded in gaining a little more distance from the latest events.
Ingenieur Müller remembers a sentence of Prandtl from this time: ''Do you know, it isdifficult to bear such a loss, but life goes on; so let us work.'' He was totally engrossed inwork again.

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21. Physicists' dispute
Although Prandtl was swamped with work as before, he once more took the initiative fora statement against the NS (National Socialist) scientific policy of that time in the springof 1941. This time, the purpose was to let those men in power know his views regarding
the disastrous dispute among physicists.
In the year following Heisenberg's rehabilitation, the swelling fight between
representatives of the so called ''arisch physics'' and those of theoretical physics hadtaken a ruthless turn again. The main attacks came repeatedly from Professors Philipp
Lenard and Johannes Stark who, on 1 December 1939, had succeeded in getting a person,
who subscribed to their philosophy, appointed to the Munich Chair for Theoretical
Physics, that was originally intended for Werner Heisenberg. Since this person was an
aerodynamicist, Prandtl was consulted. He (Prandtl) expressed his opinion in words thatwere remarkably clear: Wilhelm Müller is anything but a creative spirit, and (his)appointment to the Munich chair was a mistake. He called the appointment an act ofsabotage against further technological development.
Prandtl wanted to stand up against this all-powerful Nazi group. He wrote a
memorandum of defense of theoretical physics which he sent directly to Hermann Göring
in Berlin. It is not any more imaginable these days how much courage this step called for;a step that spoke out the truth which exposed the incompetence of the NS leadership at
judging the meaning of scientific knowledge, and which stamped its faithful supporters asincapacitated bunglers.
A contemporary colleague, the aged physicist Friedrich Hund,11 whom I met recently,
brought up this point in conversation. He remembered the courageous step of Prandtl
with much appreciation.
Following is the text of the letter of 28 April 1941 to the then Reichsmarschall Hermann
Göring:''Warding off of a serious danger to the rising generation of German physicists.
''In short, it boils down to one thing, namely, that a group of physicists, to whom the
Führer listens, is raging against theoretical physics and defaming the most meritorious
theoretical physicists. This group forces the award of professorial positions, and does so
by reasoning that modern theoretical physics is a Jewish invention which is to beeradicated and replaced by ''German Physics''--- something they cannot do quickly
enough. I have explained what this means in the accompanying annex. It is indisputablethat theoretical physics is an indispensable subject for training the Führer's rising
generation of physicists. It is up to them to arrange the entirety of physical facts into a
logical order and consequently to develop laws. The technical physicist can then produce
new designs methodologically and make predictive calculations regarding its working.
11

Translator's note: Friedrich Hund died in 1997 at the age of 101

141

The training of physicists without theoretical physics is apt to produce efficient, average
workers, but not leaders who have an overview and mastery of the entire field.
''The common characteristic among the group of physicists mentioned, who are led byProfessor Lenard, is that its members lack the capacity for precise critical thought basedon mathematical foundations. Insofar as they are not in a position to judge works ofmodern theoretical physics critically, which would require a relatively advanced level ofmathematical expertise, they are uncertain about the indispensability of the subject. In
contrast to this group, the necessity of theoretical physics is recognized unequivocally by
all physicists who have a sound knowledge and understanding of the subject, who possess
the necessary mathematical tools. I would like to ask you, respected Reichsmarschall, toconsult, on the basis of what I have written (in the annex), two well known physicists
who work in industry, Professor Ramsauer, Head of the research laboratory of AEG, andProfessor Joos, chief physicist of Zeiss-Werke, who, by virtue of their positions are
sufficiently unaffected by the terrorizing behavior of the Lenard group. As far as I am
concerned, since objections could be raised that I am not a physicist, I would prefer toremain anonymous in this matter (when I was younger, however, I completed a doctorate
in physics and since then have followed its development with great interest, which meansthat I am not entirely lacking in understanding of the subject).
''The harmful sloganeering of the group of 'German physicists' that I mentioned earlier,namely that modern theoretical physics is a Jewish invention, has caught the attention not
only of the Ministry of Science, but also of the leaders of the student body; as I suggested
earlier, it has engaged in violent attacks on the most meritorious and esteemed
representatives of theoretical physics, and drives students away from the subject. In theimmediate past, it has sought to assert itself by bringing about a professorial appointmentthat is so unbelievable that it cannot be said to be anything but meaningless - except when'meaningful' is understood to mean destruction...''
Attached to this letter, in which he requested that Hitler be informed about the matter,
Prandtl had enclosed an eight-page paper on theoretical physics explaining its scientificfoundations. This paper is given unabridged in the annex. Copies of this manuscript weresent to several people belonging to the circle of physicists. Here is one reply:
Professor Dr. Joos, Chief Physicist at Zeiss-Werke, Jena, wrote on 5 May 1941:''For a long time I have not had such joy as I had through the letter a copy of which you
sent me! At last one has the hope that the top echelons see the danger. You have earned aposition of merit for championing the cause of physics, regardless of whether your paper
will be effective immediately or otherwise! I, for one, find your account of theoreticalphysics simply wonderful!''Prandtl's letter of attack had been a certain kind of a signal. The physicist mentioned in
his letter, Carl Ramsauer, who had been elected to the chairmanship of the PhysicalSociety (physikalische Gesellschaft), sent to the Ministry of Education an extensive
cleverly worded memorandum on 20 January 1942, in order to counteract the misdoings142

of the favored ''Lenard Group''. His arguments were respected and were indeed
successful.
A. Beyerchen [7], reporting on this, writes: ''Since summer 1942, Göring's ministry lent
its support to keeping the physicists working in this area free from further politicalinterference.''14322. Journey to Romania
From 29 April up to 14 May 1941, Prandtl followed an invitation from Professor
Valcovici, an earlier doctoral student of his, and undertook a journey to Romania to give
several lectures there.
From Prandtl's report:''Considering that the journey to Romania would necessarily retardsome very urgent work, I had considerable reservations against this journey prior tostarting, and was afraid that its outcome would not compensate for the loss of time.''In spite of this doubts he started on the journey on 29 April 1941. He flew from Berlin to
Bucharest.
To his daughters on board the aircraft: ''We are traveling very comfortably over anenchanting landscape of white cotton-wool, with cloud towers scattered here and there;
over us the blue sky. Now, mountains are coming again, behind which the sheet of cloudis torn apart. Now without clouds, (the river) Elbe, mountains, then Prague, friendly
landscape, dam with romantic forts, wavy land, long villages.''
Professor Valcovici received him at the airport in Bucharest.
Excerpt from the report: ''1 May: Today is first of May. All shops are closed; but there
are street vendors with flowers, oranges and the like (sitting on the pavement or standing
bare footed). The street scene is not uniform in appearance: civic buildings in European,and commercial buildings in American style (7 to 10 floors), many broad roads. In theafternoon, during the strolling hour, there are so many people going about their way that
one can move forward only slowly. Added to that there are many cars (gasoline is insurplus).
On return he wrote the report on his lecture tour mentioned earlier. From this report, I
will give some excerpts that appear interesting to me:''My journey to Romania, on the orders of the Reich's ministry for Science and Education,
was undertaken from 29 April to 14 May. The following lectures were given:
1) A general lecture ''On Fluid Flow research (Strömungsforschung)'' at the Faculty ofMathematics and Sciences.
2) 3 lectures, each of two academic hours, for students on the subjects ''Compressible
flow'', “Small viscosity, particularly boundary layers'' and ''Turbulence''. All the lectures
were supported by a number of slides and two by a movie film.
3) On 9 May, a general lecture at the Technische Hochschule (Technical University) in
Temeschburg.

144

The 10th of May was a Romanian national holiday (Unification Day) celebrated by a big
march of school-children and a military parade that I witnessed, in accordance with thewishes of the Romanians.
The lectures that were announced through posters and in newspapers, and by invitations
sent out, were well attended in both places. There were speeches in German first, in
Bucharest one by the Dean of Science Faculty, and one by my earlier doctoral student
Professor Valöcovici.
Welcoming speech by the Dean, Professor San Jonescu:
Ladies and Gentlemen, The Science Faculty of the University of Bucharest had the honor
up to now to receive two esteemed German professors as its guests, Professors August
Sieberg and Adolf Butenandt, whose very interesting lectures have left behind a lasting
imprint.
Now, Herr Dr. Ludwig Prandtl, Doktor honoris causa, Director of the Kaiser-Wilhelm
Institut for Fluid Flow Research and Professor at the Göttingen University, has been kindenough to follow our invitation.
Herr Professor Prandtl will be giving a series of lectures in his area of research during his
period of stay in Bucharest.
Today’s subject is fluid flow research. Respected Herr Professor and Colleague,Your lecture is of interest not only to mathematicians and engineers, but also to us
biologists, since the same principles and laws that guide movement in the inanimate
world, also govern many aspects of life in the world of living organisms, animals as well
as plants. And even more, I could assert that finally these principles find application inmatters concerning settling and organization of the different arms of a society or a nation.
I am therefore convinced that the important messages in your lecture will be followedwith much interest and attention by the audience. As Dean of the Science Faculty I havethe duty to draw attention with a few words to the necessity of closer and closer GermanRomanian scientific co-operation. As I have often said on such occasions, and I repeat
with the same conviction, it is primarily working together in science that unites different
people and nations with each other.''
Report on Temeschburg:''In Temeschburg there were, besides secular dignitaries, clerical dignitaries present too,among them the orthodox Bishop, who came to the reception that followed and expressed
his joy over what he had heard and seen.
Professor Valcovici was kind to look after me during my entire stay in Bucharest. He
showed me around the city and the university, and also his own institute of pure andapplied mathematics with quite a high standing. On the afternoon of 1 May he organizedin his beautiful house a tee-reception in my honor, attended by large circle of ladies and145

gentlemen of whom I had the impression they were in the highest circles of the Bucharest
society (many university professors, different had-been-ministers, Romanian officers).
Besides these, the German Embassy was also represented, the last through Prince Solms.
The gentlemen in Temeschburg also took care of me. I was received at the railway stationby the dean and a few professors, and also by a delegation of ''German Folk''(Volksdeutsche), and was accompanied to a small ''Pension'', since the big hotels were all
occupied by the German army (deutsche Wehrmacht). One sees many teams of Germansoldiers (military) and officers on the roads and also in the pubs.''''On the streets of Bucharest there wern't any signs of unrest that could be made out. But
there is supposedly much hoarding going on. Food in the eating places, and even beer andwine, that is grown within the country is very good and meets even spoilt demands.
Meatless days have been introduced, but ham, smoked tongues and the like are notregarded as meat. A noteworthy way out has been found to meet the shortage of flour
prevalent even there, which is that only old bread rolls (of which naturally less is
consumed than the fresh stock) are permitted to be sold. Besides, rationing has been
introduced, with two days of maize bread (corn bread).
During conversations with Romanians their big worry comes to the surface that they had
to give away different parts of the country, and the point emphasized above all is thateverything else, other than acceding such a sizable Romanian population to Hungary,would have been bearable (in 1940, an area of ''Siebenbuergen'', with a population of one
million that was lost by them to Hungary in 1920, is returned by the second arbitration ofVienna). Their hope is that a different solution will be found by resettling. On the return
journey through Hungary I had a conversation with a Hungarian from this returned area,
who naturally held the opinion that even the rest past belonging to Hungary earlier had tobe returned to Hungary.''
The return journey by train enabled Prandtl to stay both in Budapest and Vienna. On 15
May he returned to Göttingen in a state of considerable exhaustion.
In the year 1942, on the 10th of November, Prandtl was awarded the title of an honorary
doctor by the University of Bucharest.

146

23. The last war years
At this juncture it appears important to me to characterize Prandtl's attitude towards
awards of honor: Whoever is of the opinion that Prandtl, who received honors among
others from the NAZI-government too, and therefore felt very close to the government onthat account, would not be in a position to convince those who knew him of such guesses,
whether they belong to the circle of his colleagues, co-workers or friends. He did not
attach much value to these certificates of honor. They came in to his residence and were
stowed away in drawers without his ever mentioning them again later.
Let a few words I remember well from those years testify as to how little such honors
meant to him. There was a "Ludwig-Prandtl-Prize" instituted for school children who
stood out at making airplane models. It was awarded annually to the most outstanding
young designer and carried a sum of 3000 RM (Reichsmarks). At no time was there any
mention of this prize at home. And so it happened that my attention was drawn to thisprize from someone outside: "Your father has indeed become quite popular with the
Göttingen population through the Ludwig-Prandtl-Prize that will be awarded every year.
Didn't you know that? Such news appears in the newspaper even here."Pushing the research work ahead, regardless of the political situation in Germany, wasthe only internal prime mover of significance that was effective. Furthermore, he waslonging to be able to finally finish up a major work. In the year 1942, the third extended
edition of his text book "Abriss der Strömungslehre" was published, a book that had
appeared under the title "Führer durch die Strömungslehre" in Vieweg-Verlag [27].
Later, this title was retained by his former students Professor K. Oswatitsch and Professor
K. Wieghardt who prepared a revised and updated version of the book. Ever increasingtasks made heavy demands upon him, yet he remained the simple and benevolent person
he was, always ready to stand up for a good cause. Just to give an example, in spite of theload of work he was carrying, he was committed to seeing through the dissertation of a
doctoral student who was sent to the Russian front. The reply of the doctoral student,
Hans Böhm, is available.
17 January 1943:
Respected Herr Professor:
Just now I came from guard duty. A delightfully clear moonlit night, such as this one thatcan be seen only in Russia, shortened the hours there and set my thoughts running. I went
through your kind letter again and was very happy. Your book is now ready and I will geta copy of the same! I hope you will believe me, Herr Professor, how much happiness thatgives me. I wish to request you to send that book to my home address since, finally, I will
be getting leave in early February. The book will of course come with me to Russia--something else will have to make way for it in the back-pack.
I am most delighted that you want to go through my dissertation, since I need notemphasize how dear this work is to me! You may want to make changes to the same,147

hopefully there aren’t many corrections. Actually I often think on what I ought to havedone differently. But errors and improvements are seen only in hindsight."
2 February 1944:"The permanent migration and disrupted life at the front made it impossible for me towrite a reply to your kind letter, and I am hurrying to thank you for your response to mycomments. I hardly venture to think of success whilst I wait for the decision. . .
Your Hans Böhm"
In the year 1943, in several letters my father writes about his trips to Berlin where he paid
visits repeatedly to his higher authority, the Kaiser-Wilhelm-Gesellschaft, since
discussions in person were preferred. On 4 March he had the experience of an air-raid.
The path to an air-raid shelter in a basement leading through a flight of stairs in darkness
proved to be a stumbling block for him. He fell and was injured on the head. He was thentaken to a doctor who had to stitch the wound without anesthesia and wound a big
bandage around his head. We were shocked to see him when he returned to Göttingenwith such a bandage on his head. But he only laughed a little and said there is no reason
any more to attach importance to the injury now. However, he had a certain feeling of
being satisfied with himself that the doctors, after putting on the stitches, had expressedadmiration for his courage that they had not expected of a man of his age.
In spite of his advanced age, he was deeply engrossed in his profession. His guiding
principle was to put his faculties for work towards the cause of progress in science as ofdate, although there was steadily increasing uncertainty regarding the near and distantfuture.
We had yet to survive the last months of war, of course naturally with night air-raid
alarms sounding frequently. Although Göttingen was mostly spared from destruction, themany hours that we spent at night in the basement brought in much unrest to our lives.
Göttingen saw the first bombing on its city area in November 1944, and the order to seek
shelter from air-raid in the basement was naturally taken seriously. Every further raid wasa new warning.
With the optimism of youth that does not weigh the uncertainties associated with the ofpassage of time when their meetings appear to stand in the course of destiny, my friend at
school Helmut Vogel and I decided to enter the bonds of marriage. There were therefore
wedding bells ringing again in our house in the year 1944. Already during theengagement period a warm hearted relationship had developed between the father-in-law
and the son-in-law. The relationship with my husband's mother and sister, a talented
painter, grew soon to be equally warm. They came down from Bremen to visit us often. I
have still in front of my eyes my mother-in-law and my father sitting at our piano,rehearsing to play music for four hands. He liked the cheerful and lovable nature of theBremen lady who had a very sympathetic understanding for every one of us.

148

The spontaneity with which my father could catch a musical phrase is evidenced by asmall record that he has kept. He had noted down the score quickly on listening to themusic over the radio in order to retain the entire movement in his memory.

G.F.Händel, Concerto grosso g-minor, 3 (?) movement.
In my opinion, the most beautiful of all concerti grossi!
16.4.44, heard on the radio. (signed) P
In the last year of the war, 1945, one hardly undertook any travels for visits. On 4
February 1945, when he completed 70, there were only a few who had come in person tocongratulate and extend their best wishes. I well remember how Professor SchulzGrunow had not shied away from traveling in spite of the difficulties and risks involved
at that time in order to congratulate my father, and how he (my father) was pleasantly
surprised and welcomed him in our home.
Several former students and colleagues of his honored him by a Festschrift [51] that
contains 20 technical articles on applied mathematics and mechanics. Due to the thenprevalent circumstances of war, the Festschrift could be released only later. Professor W.
Tollmien of Dresden wrote an article of introduction that can be given here only inexcerpts.
"It is in deep respect and love that a person whose influence on mechanics during its longand illustrious history has been epoch making is being felicitated on 4 February. On thisday Ludwig Prandtl is completing his 70 years of life. . .
The work of Prandtl could not have unfolded itself with the glory and made the impact it
did, if he had not, out of his own passionate commitment to science, aroused in his pupils
and co-workers in large numbers a similar passionate commitment to scientific research.
His goal was not so much a brilliant "Apercu" but a systematic study in depth toilluminate an entire range of questions involved, which could be achieved only by the149building up of a school. With the steady building up of the Göttingen institutes a large
number of co-workers joined the many doctoral students who worked with Prandtl over
the years, and they shared the benefit of stimulating exchanges of thought with Prandtl inpersonal contact. During such discussions Prandtl consciously avoided arresting thedevelopment of potential research workers through his towering scientific personality. A
meaningful question the answer for which appeared within reach was raised, and somepossible routes for finding the answer for the same were presented for discussion. For the
rest, Prandtl, with the patience characteristic of a true pedagogue, let the research worker
develop his individual abilities in his own way, sharing the inevitable setbacks andencouraging him to overcome the difficulties. The levels Prandtl set for the research work
were very high, true to the Georgia Augusta tradition. A brief word of appreciation by
him was the highest reward that could be earned by a young research worker. Everyone
who, like the author of these lines, was fortunate enough to work with him for some time,
will recall with gratitude the common intellectual bond that unified the cause pursued andthe respect for the personality of the Master.
Unequivocally but also without envy, Prandtl is regarded by experts since a quarter of acentury as THE leading research worker in the field of mechanics. It is no less a surprisethat, after such a monumental performance, he has not in the least turned away from
active scientific life on the threshold of his eighties. In contrast, in the last few years
Prandtl has taken over new responsibilities of leadership in the organization of scientificactivity of his country, and his own pioneering research work is not taking rest.
What could his colleagues and friends therefore wish better on 4 February 1945 forthemselves and for the person to be felicitated than that his creative powers remain
undiminished for quite a long time to come!"
Professor J. Ackeret (ETH Zürich) also wrote on the same occasion an article [2] fromwhich I am quoting only excerpts.
"Prandtl has enriched technical mechanics with entirely new features of his own. When alayman speaks of research, he does so usually in the sense of a confusing array ofcomplicated apparatus and costly instruments. But Prandtl made his biggest discoveries
with surprisingly primitive facilities. His Boundary-Layer Theory that removed thetraumatic difficulties of mathematical unsolvability of the viscous flow problem at one
stroke, Prandtl found with an apparatus that perhaps cost 40 Francs (Swiss currency) and
was driven by hand. How right he was when he told his co-workers on one occasion: 'It is
nice to have such a big telescope, but the main thing is the man who sees through it.'…
In the era before Prandtl, hydro- and aeromechanics were in a state of incipient
petrification: it looked as though nature was hiding herself behind mathematicaldifficulties. Keeping steadily in touch with experiment, Prandtl found the way-out. Witha sense of unbelievably imaginative intuition, he dropped from the general problem justso much that the essential features were retained and the mathematics just sufficed tosolve the remaining exactly and neatly, and all this in a way that led to results usable inpractice… His wealth of ideas was so profound that he gave them freely without fear of150

losing priority, and it is easy to overlook his contribution entirely when the contributionsof his numerous pupils are somehow put together. . . Those who were fortunate to study
and work with him would remember him not only as a great scientist but also as abasically kind and benevolent person and a fatherly friend… "The journal Luftfahrt-Forschung (Research in Aeronautics) published an article ''Ludwig
Prandtl 70 years'' [19] without naming the author, from which I quote:''On 4 February Ludwig Prandtl, who is not only the most well-known and successful
scientist in aeronautical research but is also heading its organization for a few years now,celebrates his 70th birthday. The festivities are held at a lower key due to the times andaccording to the wishes of the felicitated, than they would have rightly been during peace
times. But it is a day for everyone in aeronautical research to reflect for a while on how
decisive an influence on modern aeronautics his thoughts have exerted. We are gratefuland happy that Prandtl is crossing the threshold of Biblical age as an active researcher. . ..
One would probably expect that Prandtl, in his seventies, would gradually hand over theduties in the profession to the younger generation in order to devote himself to tasks close
to his heart or to tackle the hard problems that were left unsolved. He could have time
for all those who felt the need for discussions with the most experienced expert. They
would probably wish to go over with him again the thoughts that were occupying him at
the time of birth of his theories, which today, bear the stamp of the reknowned name, andare used more as a catchword than with deep understanding. In spite of the keen interestof all nations engaged in aeronautics, Prandtl remained during all the decades the leading
figure in further perfecting his theory postulated in 1904. Besides, he answered manyquestions arising in aeronautics that did not have an immediate connection with boundary
layers. We wish to mention wing theory and airfoil theory at high subsonic Mach
numbers, the so-called Prandtl's rule…
In addition to all this he was working on his text book that, in its revised 3rd edition, wasgiven the title ''Fuehrer durch die Strömungslehre'' (Guide to Flow Theory). Even here,
where Prandtl does not make demands of a very advanced level of knowledge on the partof the reader, he does not indulge in treading in side alleys that lead only to limited
heights but charts out routes that always lead to the highest. His vividness of presentationand comparisons capture even the advanced student, just as his lectures. It wasparticularly so when he took a pause or strayed away when it often offered the advanced
student more than the beginner. The goal he pursued was to arouse in the other a feelingfor precision in the formulation of concepts and a critical attitude.
He owes his success to his conducting experiments, so to say as if it were in a play, manytimes in a broader framework than was necessary to answer the technical point inquestion. Thanks to his attentive observation and his insight feeling forward its way, abaffling phenomenon was dissected into its essential elements often in a simple
experimental facility. In contrast, where conducting a tiresome experiment in small steps
was unavoidable, he freed as far as possible the technical task from everything of thenature of a chance. He thus, stripped off the problem from its inessentials leaving only151

the bare essentials and treated the idealized case lying close to the original technicalproblem which appeared amenable to a later theoretical treatment. Thus he separated thetechnical need from the gap in the structure of knowledge in physics, and directed his
efforts more towards closing this gap than investigate case by case in the technical task.
We find in his whole way of life this basic attitude of serving the whole selflessly insteadof the particular individual, which might fetch better rewards. Although recognized as theexpert, he remains very simple in his personal wishes. He remains true to the small
university town of Göttingen, and how stimulating for ideas the leisurely walks backhome in this town must have been, which is unknown in a large city with its time
consuming traffic problems! He could have had the final say in appointments to chairs,
but he exerted his influence only where it was asked for and where there was a fear ofwrong appointments being made. This attitude has borne fruit. His research laboratory
stayed alive in the worst of times, not only by its being the only one of its kind but also
by the reputation earned by Prandtl and his co-workers for their selfless readiness to
help.''
Besides the above, on the same occasion Professor A. Betz wrote an article with the title''Ludwig Prandtl zum 70. Geburtstag'' (dedicated to) ''Ludwig Prandtl on the occasion ofhis 70th birthday'') [6] that however appeared only in April 1947 in the journal''Forschungen und Fortschritte''. I will quote one paragraph:''Prandtl always strives for a penetrating treatment of the problem on hand, which has
almost always led to the goal of really understanding the phenomenon and trace it back tothe basic physical laws. Furthermore, Prandtl has the capacity to be acknowledgedunreservedly as the leader by co-workers and outsiders alike, and so chart out the routefor scientific work for the whole world. Unusual clarity of thinking and selfless devotion
to the task, free of all selfish thoughts, are the foundations that enabled this way ofworking and the big successes.''15224. The end of the war
I wish to write here of an event in the family: A few months before the end of the war our
daughter Agnes was born. The grandfather was extremely interested in the developmentof the grandchild. When he came home, he never failed to see how she was and observed
her characteristic movements with loving attention. He often sat beside her with asketching pad and drew the small head of the baby. He also kept a table to monitor theincrease in her weight. The young father could take part in the happiness of the family
only during a short leave from the front, and so the grandfather took over upon himself tobe a little of a substitute for the father. He wrote to my sister in Munich: ''Our small one
gives me lot of happiness by its liveliness and intelligence and its cooperative nature''.
In the meantime the last phase of the war had set in. We confined ourselves to one of thethree big living rooms in order to save fuel for heating. Of course my father was notwilling to do away with the piano that was in the drawing room. We therefore moved it tothe office furnished as a living room. Hardly did a day pass by, without the beautiful
instrument being played by him. Everyone who had heard Prandtl play once, listened tohis musical ideas with rapt attention. Once, when very special harmonics blossomed fromthe different keys, there were words of appreciation from us. He waved aside ourapplause only saying: ''I played it only for my dear Gertrud.''
The war was coming to a close. As the front of the enemy's troops closed in, the districtauthorities planned the blasting of all scientific institutes. In order to prevent this, some
professors who were conscious of their responsibility decided to arrange for a meetingwith the Gauleiter Lauterbacher. An agreement had been reached between them that heshould be approached in order to negotiate with him. Göttingen was in an especiallycritical condition for another reason. Twenty four military hospital divisions had been
established there, which could not be possibly evacuated. The book ''Göttingen 1945 End of the war and new beginning (Kriegsende und Neubeginn )'' [11] reports on thismission, of going to see the Gauleiter:''On 31 March 1945, in the afternoon, Professor Plischke went with Professor Prandtl, acolleague from Königsberg, Professor Baumgarten and a Göttingen lawyer, Dr. Beyer, toLindau near Katlenburg, where Professor Osenberg of the Technische HochschuleHannover was the director of the Four-Year-Plan Institute for Fabrication Processes(Vierjahresplaninstitut für Fertigungsverfahren). In the morning of the next day the four
gentlemen traveled with Osenberg to Rothenkirchen near Einbeck to see the Gauleiter,
but could talk with him only at noon. They expressed their concerns about defending
Göttingen and the consequences arising therefrom. Lauterbacher promised he would getin touch with the Reichskanzlei to pass a declaration that Göttingen, as a town of science,
should be left out of the battle area.''
When the men, immediately on their return, looked up the Kreisleiter, he had alreadybeen directed not to revoke the order to blast. The professors were stamped by him as''liberal defeatists''. I remember that my father returned home very tired from this venture,
being taciturn and laconic.

153

Through the initiative of courageous citizens and sensible civil servants of the cityadministration the city was handed over without a fight.
The day of 8th April, a bright Sunday, is still vivid in my memory. The latest instructions
we were given, had asked us to stay in our basements, after the previous plan calling us
to assemble in open air far outside the town, had been given up. The previous evening afellow resident of our building, Frau E. Oesterheld, who had fled earlier from Berlin,came to us. She has made a note in her diary of this visit to Prandtl on the day before
surrender.
7 April 1945:''He was sitting in his office-room at home that had nothing of a home-like coziness. It
was furnished soberly and office-like, with big card-board boxes on the walls. Only a big
piano and a few good oil paintings lent the room some glamour. He was sitting at thetable which was covered with a table-cloth made out of oil-cloth, and had just heard thenews over the radio. His expressive, venerable, scholarly face was filled with sorrow andworry. I told him of the call of the Party asking women and children to assemble on theRohns hillock at five in the morning, and asked him what he would advise. I did not get
any sensible reply at all. Obviously he was strained by the events rushing in, and wastotally incapable of taking a decision either for himself or others. His daughter Frau
Vogel came in, and we finally decided, after some dilly-dallying, not to join the womenand children leaving the town, but to stay in our air-raid basement-shelter and await thesurrender.''E. Oesterfeld writes on 8 April as follows:''Sirens announcing the alarm about the enemy sounded around noon; all the inmates of
the house went into the basement. We sat there anxiously for a long time without
anything happening. After all, was the town handed over without a fight? Suddenly
something crashed, the building shook and the window panes came down with a rattle.
The rumble still continued, the impacts could be heard clearly. Suddenly everything
became quiet again. Professor Prandtl said: 'I will go up now and see how things look up
there. And, if something happens to me---I am already old, I do not matter any longer', headded in modesty.
The old man then came down again. 'It looks terrible, it was good you didn't stay upstairs,
otherwise all of you would have been buried underneath the rubble' he said to the family
that lived in the 2nd floor. 'Obviously it was a grenade, it must have hit the gable first;
there is debris on the whole staircase.''
Although, as said earlier, it had become quiet again, we were under shock and remained
sitting in the basement for quite a long time. From there, through the window at the
ground level we could see the never-ending chain of tanks rolling by. Had the war really154

ended for us? We saw the occupation by Americans, as a fortunate lot. We mustered up
courage afresh and returned to domesticity in order to prepare food.
The next day it was of supreme importance to my father to go to the Institute. What heexperienced there on that and the next day is something I didn't get to know. He was very
silent and introvert. He was missing, as in all these years, his companion in life to tell her
what he had experienced.
Very much later, I did learn through the narrations of others that the Americans, before
they occupied the Institute, got handed over to them all the scientific results that were
kept secret during the war.
Then they took over the Institute completely under their power. My father was denied
entry for several weeks. However, he was required there, once during the first week. He
was picked up at home and was taken in an open military vehicle, guarded by six
American soldiers. Neighbors who saw this, were asking with concern, where theProfessor could have been taken. After the elapse of a few hours, he was brought back inthe same vehicle. There is a report of Prandtl himself on this incident [5]:''One day I was taken in a van to the AVA grounds by armed soldiers. The leader of thesoldiers, a German-speaking Jewish officer, wanted a statement from me as to what wasthere on the grounds, and was at first very much disappointed on what I could tell him.
He wanted to know about the prototypes of the airplane engines that we were supposed tohave built in Göttingen. I had to tell him that we had only conducted studies of parts - forinstance compressors - regarding the lay-out of their best shape.''But for the rest, apart from these incidents, for the first few weeks my father and I, likeall families those days, had to procure food, which took much time. In order to buy breadthat was allotted to us on the ration stamps, one had to start out early at six, at the hour oflifting the curfew, to queue up at the bakery, since bread was sold out shortly after eighto'clock. How often did my good father go on this errand for us both since I had to lookafter our baby daughter. The maid who was helping us in our household, had returned toher village even before (Göttingen's) occupation by the American troops. Carrying on oursmall household, required much common effort. Since neither gas nor electricity wasavailable, and there was an urgent need for firewood, I got a first stock of wood in awheelbarrow from the nearby woods of Hainberg. No one cared for the problems that theother person had. In all households, just as in ours, the shortage had to be met throughfull use of effort and time. In the courtyard we then sawed the round logs into small
pieces in arduous teamwork.
Shortened hours of curfew and regular supply of food stores brought some relief alreadyin May. In spite of it, the situation was still tense. The military government had suggested
to the mayor to get loudspeakers installed in the town in order to keep the public
informed of the news, and mayor Schmidt wrote in reply: ''The people are very hasty andnot in a position to listen with attention or read the announcements posted. Standing in
the queue at stores takes several hours of the house-wife.''155

Professor Nikuradse turned up unexpectedly at our house and announced he would
arrange for a cart-load of wood. The wood was really delivered at our door the next day.
Soon thereafter, young people from KWI (Kaiser Wilhelm Institut) who were unemployedcame and sawed the wood into pieces. The firewood stock that was piled up in our yard atthat time was substantial.
It was strictly forbidden to continue research work in aerodynamics. Instead of resigning,
Prandtl now started addressing meteorological problems. Meteorology had indeed been
one of his special fields of interest for a long time. He used the weeks at home forworking intensively. Now and then, a colleague came home to tell him where mattersstood and to talk over the possibility of a new beginning.
Ministerialdirigent A. Baeumker was among these visitors. There was a long and lively
talk. The guest had to make do with soup for lunch that I had boiled in the same room on
the oven. Baeumker who was an airplane spotter in the First World War, and then adelegate at the disarmament conference in Geneva had a vast organizational experience.
Now he was already thinking of new plans for the distant future of the AeronauticalSociety (Gesellschaft für Luftfahrt).
In the year 1949, A. Betz and L. Prandtl wrote, from their memory, a comprehensive
report on the matters of the Institute in spring 1945 [5]. Here are some excerpts:
A. Betz: ''An important event was the visit of Professor v. Karman on 14 and 15 May,
who came to the AVA with a group of esteemed research scientists. It is perhaps here thatthe possibility first came up for discussion, to allow the Directors and their personnel toenter the Institute premises once again. Since research work was forbidden on grounds ofprinciple, v. Karman saw an alternative way for keeping the scientists occupied again. He
suggested that they write reports on their research work during the war years in theservice of the occupying power.'' These monographs were later translated into English.
L. Prandtl: ''Visits of American experts started to be rather frequent, and I had to show
and explain to them my special institute, Building no. 3. ...I requested them to mediate
for us to be permitted to move about more freely within our own Institute. But mattersstayed where they were, in that we had to be accompanied by armed soldiers in our
Institute.''Later, I was told of a statement by Prandtl that characterizes the absurdity of the situation
to which he was exposed: With a smile he spoke to the soldier who was always following
him with a machine gun: ''Is the soldier perhaps afraid of me?'' Embarrassed, the soldier
explained to him that the rules were so.
Prandtl: ''The scholars and the experts came in increasing numbers, and I felt more andmore like a museum attendant, who had to explain in roughly the same words, the samething again and again (and of course according to the context told the same small jokes).''156

According to the statement of a Mitarbeiter, one day documents were searched that ayoung scientist had hidden in a secret location. He (the young scientist) was rather
alarmed, and had probably every reason on imagining the consequences if he would haveto confess to the military power. ''Regarding the documents I will take it on myself'',
Prandtl told him, ''they won't behead me as easily as perhaps you.''
Professor Betz too was called equally often for guided tours around the Institut, foranswering questions and giving explanations.
Betz writes: ''The questions asked during these guided tours often gave us an insight into
matters of fact that were surprises to us. For instance, most of the Americans could notunderstand that we were mostly doing fundamental research. Even the big difficulties
with manpower and material during the war were often unimaginable for them. The
question was asked several times as to why such an important facility as the big
refrigerated tunnel was not completed fast.
Some other questions indicated an ignorance of many matters known in Germany
although the people asking the questions gave an impression of being capable scientists.
For instance, the question came up again and again, as to why we built swept wings, andit required long and repeated explanations until the advantages of this type of wing on
approaching sonic velocity were understood. Now swept wings are foisted as a big
American invention.''Prandtl was very happy when the occupation authorities permitted him to enter theInstitut premises regularly again, after being forbidden from entering for eight weeks.
However he was required to obtain a permit at the hour of commencement of work, andone again at cease work. A grotesque requirement for the Director of the Institute! One
day Prandtl innocently asked: ''Could I also get a permit valid for the whole day, like theone our Institute's messenger gets?''
On 8 June 1945 he wrote to my sister in Munich:''In my Institute, work has begun again on a small scale with a third of the personnel.''A few of the talented younger scientists soon found positions for work in America or
England where they were offered very good openings for continuing their scientific work.
I wish to mention here one small thing. At that time, a loaf of bread was given to theemployees of the Institute every week. My father liked the taste of the ''Institute bread''very much; he was keen on cutting a slice of it every day which he tasted as in a church
service. Of course he distributed it too. But I observed that he was very cheerful when thebread was in front of him on the dining table. It was certainly not the plentiful supply forthe mouth that gave him satisfaction, it was this ''Institute bread'' that had a symbolic
value for him. After he had been locked out for weeks, he had a feeling of tranquil
pleasure that he could work again in his spiritual home, the Strömungsinstitut, although
under more difficult conditions.

157

Prandtl wrote his English colleague G.I. Taylor in detail on the post-war events in his
institute.
28 June 1945✳:''My institute survived undamaged through the war. However, there is now
a lot of damage because American soldiers were accommodated here for several weeks.
Only after the beginning of June were we allowed to enter there. The Allied Committee
told us what to do. We were allowed to make some repairs and to write reports for Allied
Committee. We were also permitted to continue certain projects which remained
unfinished during the war, and on which reports were expected. So far we have not been
permitted to begin new work. Yet we hope soon to be able to investigate problems of afundamental nature which were set aside during the war. We have enough such problems
to last a decade.''On 10 October 194512 to Taylor:''Any continuation of our research has hitherto beenprohibited by the Director of Scientific Research in London. For a research institute
whose mission is to extend the knowledge of its subject as far as possible this is a very
hard demand. Indeed, we see many problems that await their solutions, for instanceturbulence and near-sonic flows. Problems of meteorological and oceanographic flows inwhich density stratification and turbulent processes both play an essential part are also
among such topics.''
Although the stringent measures of the military officialdom had entirely banned scientificdevelopment, and as a consequence, Prandtl's sphere of influence had been narrowed
down, his international standing continued uncontested. A Chinese scientist who had
worked under Prandtl on her doctor's dissertation in the beginning of the forties and had
survived the war in Berlin, came to Göttingen and spent some time there shortly after theend of the war to get Prandtl's advice for further scientific work. Ms. Lu Hsin Chen thenreturned to China where she became a professor in aerodynamics later. Once, in
retrospect on her Göttingen years, she said, that Professor Prandtl had looked after her
with fatherly benevolence. The living memory she cherished of her respected mastermade her come to Göttingen with her husband again and pay a visit to his grave. We
stood together in front of his tombstone. They bowed thrice paying respect for the dead as
they do in China to revere their forefathers. In 1984 she sent me her translation of
Strömungslehre into Chinese. She wrote in the accompanying letter:
16 November 1984''I am taking the opportunity of a colleague of mine in my institute who is going toGöttingen to carry on scientific co-operative work in DFVLR, to request him to give abook to you. It is a translation of the book Führer durch die Strömungslehre of my highly
respected teacher Professor Ludwig Prandtl. I have done the work of doing the translation
in memory of the greatest teacher of fluid mechanics in the world.
Lu Schang (nee Hsin Chen).''
12

These translations have been taken from the book G. Batchelor: “The Life and Legacy of G.I.
Taylor”, Cambridge University Press, 1996, page 187.

158

25. New beginning at the university
Efforts were already under way in July 1945, at the university, to restart teaching. Due tothe denazification procedures ordered by the military government, a number of former
professors were dismissed. So, only a part of university teaching staff was available for a
new beginning. (From the ''War Diary'' of the military government of Göttingen, 8
August 1945: ''None of the 60% of the dismissed university professors filed an
objection.'')There were of course many other difficult problems that had to be solved, e.g.. working
out rules of admission of students, re-equipping the mensa, measures for procuring
housing for students. In the course of this an appeal was made to the population toregister rooms for students in private homes, asking everyone to forego rooms that were
owned but could be spared. We too, with only three of us living in our house then,registered two of the rooms that were empty as ''student rooms (Studentenbude)'' andaccepted the disquiet brought in by these young people. Soon there was hardly a house inwhich no student was housed, at least in the attic.
On 17 September 1945 preparations had advanced sufficiently enough that Georga
Augusta could open its doors to students as the first in Germany. The British Military
Government had fixed the number of students as 3500, but this ceiling was soon crossed
since it was decided to enable the combatants at war, who were released later, also to
begin studies.
Prandtl, although seventy, gave lectures as until now. Generally the students' eagerness tolearn was favorably recognized. The city had transformed itself within a few weeks, and a
new spirit of freedom was perceivable in spite of the occupation forces.
In 1946 Neue Physikalische Blätter wrote: ''With 4775 students registered in the summerterm, Georga Augusta is at the head of German universities.''Now, after the truth had come out to the full extent, Prandtl, who was deeply hurt, tried to
introspect upon the happenings of the immediate past. He decided to formulate
coherently in writing, the conclusions that he had come to, particularly with regard to theprospect of further scientific work. He addressed a letter to the Education Officer, Mr.
Bird, to whom he wished to communicate his reflections. He called his memorandum:'Thoughts of an unpolitical German on denazification.'
Prandtl himself had, as already related, refused outright every kind of membership of theParty, and so had no incriminatory charges against him that could come in the way of a
fresh start. But he could not, as it was in his very nature, ward off feelings of sympathy
for some of those who were indiscriminately sentenced only on reasons of their party
membership with no political interests or activities. In his always humanitarian stand, heconsidered it necessary to give clarifying explanations to the occupation power on the
coming into existence of the NS-State and its consequent development mechanisms.

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Possibly these explanations enabled a more favorable judgment to be passed in somecases of incrimination.
In the meantime there have appeared many publications on this subject which have been
keeping our (particularly Germans') thoughts increasingly occupied although 40 years
have passed since then.
Below is the letter of 14 March 1946:''Respected Mr. Bird,
Following your suggestion I have drafted a memorandum on the question ofdenazification that could be suited for publication in an English newspaper… Should
there be some point which you wish to talk over with me I will be glad to be available to
you at any time.
Respectfully yours,
Ludwig Prandtl''''Thoughts of a nonpolitical German on denazification
Preliminary remark
The question of future political development of Germany, and in particular that regarding
the best procedure to eliminate all elements that could obstruct this development, is
occupying the thoughts of many in Germany today. The author of this memorandum is a
professor at a German university. He is an engineer and a physicist, and is most probably
known to the English specialists of his area. He is more than 70 years old. His age and thefact that his life has been dedicated to scientific work, probably protect him fromsuspicion of being an extremist of any kind. Indeed he has never wanted to have anything
to do with politics, but on the basis of the sources available to him, has tried to form animpression on the questions mentioned above that he would like to share.
The state of affairs in 1932
According to the Weimar constitution, the German parliament was elected through listsof the Reich (Reichlisten) that were presented by the individual parties. This procedureencouraged the formation of a huge number of small parties, and this was reflected in the
results of the new elections. In these circumstances, a parliamentary majority could beformed always only through co-operation of parties with programs widely differing fromeach other. The governments so formed stood, therefore, mostly on a very weak footing,and had to work their way through permanently through some compromise or the other. It
is therefore understandable that the Government (of the day) was not up to the task ofdealing with the problem of as many as seven million unemployed in the ultimate stage,
and a further seven million underemployed. Besides, the rural population was strongly in160

debt due to forceful imposition of artificially low prices for long, coupled with high rates
of taxation on its products. They were also severely oppressed by the harsh methods ofcollecting these taxes, which they could not resist, being still divided and so in theminority relative to the industrial and other urban population.
With this economic misery thus ruling in both cities and villages, it was not a surprisethat the extreme parties---the communists on the left and the national socialists on theright---steadily gained power, with the two often in violent conflict with each other. The
rural population, to whom Hitler promised deliverance from debt and protection of
inherited property, followed him in large numbers. Many of the unemployed, who did not
like the communists' methods, also turned towards Hitler since he promised creating
employment for them. These developments headed towards a duel between the two
extremist parties. Many followers of the centrist parties considered National Socialism tobe the lesser of the two evils; they were afraid of a Bolshevist rule along Russian lines if
the communists came to power. It was thus that it happened that Hitler could gain the
support of a majority to form a government in 1933. The Reichspräsident Von
Hindenburg, who was a man of honor, asked him (Hitler) to be the Chancellor of theReich, in accordance with democratic processes; but this earned further sympathetic
voters for Hitler.
The psychological situation after NSDAP''s take over of power
In the beginning, Hitler exercised considerable restraint, obviously influenced byHindenburg. Many of those who did not like Hitler's earlier ways, hoped that thenumerous moderate elements that had helped Hitler to attain his majority, would have asalutary influence on the way he conducted the affairs of the State. This is how the large
number of votes that Hitler gained at the plebiscite in March 1933 can be understood,
whereby the political pressure, that was occasionally applied, hardly improved thisnumber.
There was a large increase in the Party's rolls during this period. During the first few
years after 1933 the Party's composition can be characterized as follows:
1. There were Party members of many years' standing, the so called ''alte Kämpfer (theold fighters)''. (There were many among these who were failures in their profession
due to their own inadequacy, but there were also many idealists who had set
themselves the goal of fighting against the danger of Bolshevism).
2. There were other discontented people who, partly out of a craving for recognitionand partly for selfish reasons, wanted to gain influence through the Party.
3. The unemployed enrolled in the Party hoping for a betterment of their situation; andthe same was true with many in the rural areas.
4. There were also many earnest men who were aware of the shortcomings of the
Hitler system but believed that they could correct the damaging influence thatprimarily the old fighters would exert; many in this category also had the idea that
Hitler should be supported in order to save Germany from Bolshevism.

161Men belonging to the fourth group above could achieve something good in isolated cases,
but they soon came to realize they could not exert any influence on the bigger politicalissues. The step of demonstrative resignation from the Party that some of the morecourageous among them took, served only to teach the rest that they will only be
exposing themselves to the most severe persecution and losing all further influence in the
Party. Whoever believed that he should try to do something good in the small circle
around him had, therefore, to stay in the Party, and accept that sometimes he had to saythings that were going against to his true attitudes.
As these developments were taking place, Party authorities put increasing pressure on thepeople to enroll for the Party and its sub-divisions. In fact, Party membership was
categorically demanded of persons aspiring for civil-service posts. Whoever who could
not afford to renounce aspiration for such a career, for economic or other reasons, had tobow down, even if it ran contrary to his beliefs. It was much the same even with the timid
people of the older generation. And it was not rare for private employers to exert pressure
on their sub-ordinates to follow the same direction. The large number of ''campfollowers'' that emerged thus becomes understandable.
Conclusions regarding the denazification procedure that is to be aspired
This wide spectrum constituting the Party makes it inadvisable to choose a purely formal
procedure laid out schematically going by the particulars given in the Party-book or in aquestionnaire. Rather, it is necessary to base judgment upon the actions of the individual
and his overall influence. Of course, such a system is more cumbersome to handle, but
destinies of human beings are at stake, and so the bigger effort is probably worth
undertaking. The new Denazification Law in Bavaria already adopts this course. If one's
own people are involved in the decision making, the danger of individuals trying to pullthemselves out of the noose through lies is not very large. One knows one's people, and isin a position to distinguish between ''followers'' and the real Nazis. Every German
concerned about the future of his people expects that those who have a heavy burden of
blame to carry because of their doings during the past twelve years should be punishedseverely. In much the same vein, severe punishment should also be meted out to those
who used their privileges as members of the Party or of other organizations for their own
personal advantage or aggrandizement; and also to those, who inflicted much harm onsome fellow human or other through slander or denunciation. But the German people also
have a right to retain in their midst those precious people among the Party members thatshould continue their work without disruption, freed of the odium of being a Nazi that isstill stamped on them.
I do not regard it as my task to talk about the most purposeful kind of punishment (forsuch people). I only wish to say that the punishment, in terms of both location andduration, will have to be graded according to the gravity of the delict or the crime.
Possibly, withdrawal of the active and the passive voting right for a probation period
could suffice as the mildest punishment. Through this measure, we can prevent immature
or incorrigible elements from disrupting the new political advances. It would also suffice
as a measure that takes into account people's feelings against the harmless followers.

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Denazification in the universities
It should be understandable that for the author, it is the inner circle of his own activity
that is of primary concern. Here, the Nazi regime has done much damage through theentry of persons totally unsuitable for the teaching and research profession into the
Hochschule, and their arrogant assumption of power. These people, often Dozents who
were failures in their career due to incompetence, distributed leading positions in the NSDozentenbund (National Socialist Association of Dozents) among themselves. They
exercised considerable influence on the new 'calls' (appointments) in which they tried toaccommodate more ''alte Kämpfer (old fighters)''. Apart from a few highly talented
individuals, only those who were acceptable to them---through becoming a member of
the Party, or was in the SA or some similar organization---could from then on become a
Dozent. The Reich's Directorate of the Dozentenbund in Munich also exercised authority
over the Hochschul-division of the Ministry for Education, which often thought moresensibly in matters regarding the choice of suitable teachers: the Reich's Directorate,
however, could block every 'call' unacceptable to them since they were given vetoingrights by Hitler. One can thus imagine how all young aspirants, who either could not or
did not want to forgo their scientific careers, had to pay their tribute to the Party in somemanner, often in great mental agony. Those who were particularly timid permitted
themselves to be coerced to going further than necessary and became leaders of blocks or
the like, and have difficulty now in making their non-Nazi disposition believable.
The universities should demand that all those young researchers and teachers who are
valuable from both human and professional points of view, and were not activists but
only wished to serve the cause of the state and their science should be taken back oncompassionate grounds. They should not be penalized, for they had no other way to makea scientific career than through the Party that was totally assimilated into the state.
The future of the whole rising generation of German university teachers depends upon
the adoption of a policy decision in this spirit.
I can very well understand that the English, who have been used to a democratic form ofgovernment for centuries, will have much difficulty appreciating such thoughts. Only
those who have lived under a dictatorship may be able to understand the present situationin Germany.''
After this open admission of guilt that pointed out to the wrong conduct of the unpolitical
German, Prandtl, however, suggested that judgments regarding denazification be given asecond thought according to his explanatory observations. Again and again, he stood up
to help a colleague to have his past rated more justly, when they were accused ofcomplicity by the military government and sentenced accordingly.
Prandtl tried again to make the authorities of the British occupation forces understandhow differently such memberships should be judged. In this spirit, for instance, he wrote
on 14 April 1946 to Mr. Bird:

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''It is about Professor Osenberg from the Technische Hochschule Hannover, who, as you
would know, had developed with great success, the work of the planning office of theReich's research advisory body (Reichsforschungsrat). In the course of many years ofwork, he got it approved, against much resistance, to have important scientists released
from the front for research work in a planned manner. …
If there is a way to free him and other professors from internment… much good would bedone in a humanitarian spirit and for scientific occupation of these scholars.''
I wish to quote another letter in which he stood up, speaking on behalf a colleague. On 13
January 1946 Prandtl wrote a conduct certificate in the matter of the trial court caseagainst Professor H. Schaefer of Bad Nauheim whose past history as a member of theParty was under investigation.
''I came into personal contact with Professor Hans Schaefer in the year 1943 in mycapacity as the president of the research leadership body (Forschungsführung), because
the matter under consideration was issuing a call to Professor Schaefer to take up a
position to be newly established at the Munich Aeronautical Research Centre(Luftfahrtforschungsanstalt München). At that time, he was suffering due to theenormous pressure exerted by the Frankfurt Gauleiter who had set everything moving to
remove him (Professor Hans Schaefer) from Nauheim. On the occasion of a visit byProfessor Schaefer to Göttingen, I myself had a longer discussion with him. He told me
in detail, during this meeting, of the efforts of the Gauleiter to remove him from
Nauheim. Extract out of my report to the research leadership body (Forschungsf"uhrung),
8 June 1943: Professor Schaefer is trying his best to leave Nauheim since it doesn't suit
the Frankfurt Gauleiter that Schaefer is a Catholic who goes to church.
My personal impression of Professor Schaefer is entirely one of a serious scholar full ofscientific ideas. Therefore I do not have any doubts that every word in his statement canbe believed.''In his biography ''Perceptions and Confessions of a Scientist'' (Erkenntnisse und
Bekenntnisse eines Wissenschaftlers), the physiologist Professor Hans Schaefer himself
writes of his above mentioned visit to Prandtl at Göttingen [45]13:'' In spite of many trials, my attempts to tread the easy path on a different occasion, ended
in a failure, of course during the war. I wish to describe one of these trials since it permits
singing a song of praise of a great scholar.
In the meantime, I had made friends with Theo Benzinger. He thought that (my) being
taken over in the position of a Government Medical Officer (Regierungsmedizinalrat)
would be possible, and had paved the ways for the same. The person who finallymattered was Professor Ludwig Prandtl, the great pioneer of fluid flow research in13

No translation of this book is available in English.

164

Göttingen. I had decided to visit him in order to promote the plan of working at thebiologicalinstituteoftheAeronautical
Research
CentreMunich(Luftfahrtforschungsanstalt München) under the directorship of Benzinger that was still
to be founded. During the visit, that took place on 7 June 1943, I found Prandtl rather
disapproving at first. He did not understand why I wanted to go to the Air Force(Luftwaffe) now, didn't I read any newspaper? My hint that I was being forced by theGauleiter to look for a position, and that I was rather stuck in political difficulties,changed the old and surly person into a lovable fatherly advisor. His advice: Stick it out
in Bad Nauheim. It was the same advice I got from my colleague Hermann Rein too. So I
saw the end of the war in Bad Nauheim. With the moving in of the American tanks in our
town the most deadly nightmare of my life came to an end.''Dr. Hans Schaefer wrote on 17 November 1946:''Respected Herr Prandtl,
I have received your certificate, issued in my case, and wish to thank you from thebottom of my heart. The letter will most certainly make an impact.''

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26. The first post-war years
The British occupation authority had prohibited the continuation of any research work in
the individual institutes, but the Kaiser-Wilhelm-Society (Kaiser-Wilhelm-Gesellschaft)existed further on as an umbrella organization. In arduous discussions with individuals,
its General Secretary Dr. Ernst Telschow succeeded in keeping this society continue its
existence as a registered society. This far-sighted man had already transferred a part of
the general administration from Berlin to the undestroyed Göttingen before the end of thewar, and had thus laid the foundation for further work.
Even for Dr. Telschow, whose significance and influence in the years following simply
cannot be overstated, Prandtl could influence the authorities to issue a ''no suspicions''
certificate (letter of 7 June 1946 to the occupation authorities).
Dr. Telschow conducted transactions with the military authorities in Hannover and orally
reported to them on his visits to the different institutes that were in the other zones, theAmerican, the French and the Russian.
However, a clear directive, defining the purpose, was still absent. When Max Planckcame to Göttingen as a refugee seeking shelter with relatives in Göttingen, it was an
obvious thought to suggest to him to champion the cause of the research society
continuing to exist. It was known that Planck was held in high esteem by the victors, due
to his unassailable clear stand against Hitler. He was requested by a committee to take up
again the presidency of the society in spite of his advanced age (87 years). Later thesociety was to be named after him as Max-Planck-Society (Max-Planck-Gesellschaft).
Planck agreed and was ready to dedicate himself to the task of rebuilding this society.
Thus the responsibility for the many German research institutes was lying again in one
hand.
In April 1946, when Prof. Otto Hahn was released from imprisonment and came back toGöttingen, he could relieve Planck through assisting with the difficult administrative
matters. Hahn was then elected to the office of the new President.
The fluid flow research institute could be run further in this way, but not the AVA, die
Aerodynamische Versuchsanstalt. It was denuded of all its equipment---the wind-tunnels
were partly destroyed, partly dismantled and shipped off to England. However I cannot
remember my father telling me of this. It must have been very painful for him to witness
the experimental facilities that were a product of years of planning being converted into
wreckage, his life's work being destroyed through demolition. He did not live to see a
generous plan bringing new wind tunnels back to the laboratory halls. Sometimes myfather described himself as a stoic; subscribing to the philosophy of a basic ethicalattitude that teaches not to let emotions rule.
In the scientific arena, as a whole, there were on the other hand new beginnings. It waspossible to accommodate other institutes in the empty buildings of AVA. W. Heisenberg
had moved his Kaiser-Wilhelm-Institute for Physics there and shared the space with C.F.

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von Weizäcker and K. Wirtz, who in turn built up their own departments. It was therefore
not a surprise that the first Physicists' conference after the end of the war took place on 4
October 1946 in Göttingen. Although the number of participants had to be restricted due
to catering difficulties, around 80 physicists had gathered together for the conference.
One was happy that the pleasant custom of exchange of scientific ideas could be revived
again, regardless of the poor state of goods supply.
Prandtl's interests were now consciously directed towards politics. Against thebackground of the lapses in the past, he felt it a duty to reflect independently on politicalhappenings and draw consequences from them. After the political parties had establishedthemselves afresh in 1946, he became a member of FDP (Free Democratic Party).
On the domestic side, at home in Calsowstrasse, things brightened up a little for us when
my sister returned to join us in Göttingen in the autumn of 1945. She had lost everythingin Munich during a bomb attack, and we were happy to see her again in good health. She
herself was happy to be with her family again, put herself entirely at our service forrunning our household, and she was very keen to look after the aging father at the best
possible. It took a lot of time those days to procure enough food for a family. For the little
that was available on ration stamps, one stood in a queue, and that, too, in different shops.
In autumn, we collected beechnuts to extract oil, and gleaned potatoes from harvested
fields, since the main food: potatoes, was never available in sufficient quantities.
Sometimes we were fortunate to obtain precious food in exchange. With all hands pulling
together, it was easier to cope up with everything.
Even my cousin Hermann Föppl, who wanted to study in Göttingen after being
discharged from captivity, could be accommodated with us. He remembers the evenings
when he sat with his uncle at the big kitchen table and how he (his uncle) sat late into thenight going through his work. Consumption of electrical power had been rationed in sucha way that power was cut off at ten at night. But in the kitchen we had, besides theelectrical power connection, an old fashioned gas lamp. The rays of light passing fromour kitchen over to the other houses shrouded in darkness might have surprised somecitizens of Göttingen.
Then, in April 1946, my husband, too, was discharged from American captivity. He hadremained in good health; there was enough food with the Americans. Our small daughter,then one-and-a-half years old, made friends quickly with the young father.
Now we all lived, though under somewhat restricted conditions, in the same apartment.
But things could be arranged in such a way that our father kept two rooms for himself.
Shortage of space to live in was general in Göttingen so that everyone had to get used todoing with less space for living.
The meager food with which all of us fed ourselves for good, was always less thansufficient for a whole family. We still remember the piteous mealtime when nothing but a
few boiled potatoes could be brought on the table. In order to roast it, we poured a little
cod-liver oil into the frying pan. The product of our art of cooking did not agree with any

167

of us. So one can imagine our bright cheer on receiving on the next day from Professor
Courant from America a Care parcel with its rich contents on which we could run thehousehold for a long time.
Later, a few other colleagues living in America also thought of their teacher and friend
Prandtl. So almost every month, we received one such precious packet from overseas.
With these we had been generously favored, and the anxious question as to whether wewould perhaps be without stocks the next day, never came up again.
Our father took part happily in our family life. The son-in-law who used to bring inthemes on human problems in conversations, exercised a stimulating influence on the
traditionally scientific atmosphere of our house. There were then talks of a more generalnature. Occasionally, my husband noted down what appeared significant to him.
One day he asked his father-in-law in a manner that was easygoing to a certain extent,
whether he (Prandtl) understood the Theory of Relativity that he (the son-in-law), a
philologist, knew so only by name. Our father replied, with a little smile ''Yes, really---it
appealed to me straightaway so that I also became a relativist. On my reading Einstein's
first article, right at the outset I had the feeling, in fact the conviction, that this wascorrect.''
The reply was characteristic of Prandtl's forbearing attitude and helpful attention, eventowards one not very knowledgeable in science. He took the other seriously enough toconvey his appreciation through a tangible reply. This attitude of always paying respect
to the other becomes clear in a basic statement of policy to the authors, which he worded
as follows: ''The reader must be treated obligingly in order that the sections, difficult tounderstand, are bearable.''My husband has often heard the father-in-law ''preluding'' on the piano, as he (Prandtl)
called it himself. One day, when he asked him whether his music was, for him, an
occupation with higher mathematics in a certain sense, a sublime game with proportions
and ratios of numbers, Prandtl replied: ''No, nothing of the kind, most certainly not, but I
play guided only by my feelings. However, when an unexpected chord happens to be
struck, or an unintended harmony, I am inclined to follow that direction consciously.''
Basically, it is all dependent on moods. According to his own statement, he succeeded
best in improvising when there was a particular occasion, such as on days ofcommemoration or bidding farewell. (In fact I can very well remember that he delighted
us touchingly with his music on family festivities: birthdays and days of baptizing, again
and again compositions of surprising mastership.)In the course of a general conversation on outwardly success, he said he had been
specially favored in that ''what was close to my heart also happened to be of interest
during the times. One should after all profit by what one has, to the best possible. For the
rest, I have my professional ethics that makes me strive for leaving behind a work ascomplete as possible and to attracting a class of pupils who would continue this work.'' It
is proper to include at this juncture what he said about himself when my husband related168

to him once that an English professional colleague described him as ''a marvelous sort ofman''. ''He was surprised that someone, whose scientific success is the subject of talk ofso many kinds of people, appears to be not proud of it at all. I think, I can say of myselfthat in spite of so many honors over all the years I am not conceited. '' But, after a smallpause he added, in a conscientious self-searching way, as it were, ''But when I say that I
am already demonstrating that I am after all conceited. I am indeed proud of what I haveachieved, but I never make use of it.'' On a different occasion, he expressed his opinion
on his attitude in situations of conflict: ''Apparently the human being has often tosacrifice something when suppressing temperamental outbursts. I am very fortunate inthat I am very slow in such thoughts. By the time I have a grasp of the whole situation
everything has calmed down so far that I accept it calmly.''
This composure was for him the essence of an appropriate fundamental attitude. To thequestion as to what enabled him to withstand painful things, he replied again:''Composure!'' He said he underwent a very difficult time after an operation.
Sleeplessness and inner unrest had tortured him. He said he then told himself: ''I mustregain this composure.'' Whether he feels bound by the stoic ideal? ''Yes, stoic teachinghas always appealed to me- not only not to expect anything at the time of death, but also
in life. I do not believe in immortality, but I do believe that one has to lead a morally
righteous life. If there is no cause to blame oneself, then this composure becomes a partof the person. One should have sympathy for and be good to the other. One should help,
but do not expect anything, on the whole in a certain sense a stoic moral.'' In reply to thequestion if his humanitarian upbringing had prepared him to acquire this attitude, he said:''Yes, it is quite possible. But it needs a certain strength to make this attitude one's own.''
This strength is perceivable in his detached attitude towards death. In the context of aconversation on the question of life after death, he said: ''I do not expect anything formyself (Ich erwarte mir nichts). I know that one day my heart will cease to beat and mybreath stops. I have had enough time to get used to this and accept it.'' Through his
occupation with the sciences he said he had gradually moved away from the Catholicteaching in which the thought of immortality connects itself with the thought of God.
Finally, on the thought of Genesis, he replied: ''A Creator of the worlds? Well, howshould I imagine that? I do not formulate that for myself, neither do I feel a need for sucha formulation.'' In this spirit he subscribed expressively to Goethe's words: ''The mostbeautiful fortune of the thinking human being is to have researched into what is
researchable and quietly to worship the unresearchable.''In the course of a conversation on the last war, the very earnest foundation of his
philosophy of life became clear, as also his strength to stare into the eyes of recognizable
truth relentlessly. ''It is an old wise saying: The world is after all a valley of
wretchedness.'' My husband adds here from his own philosophy of life: ''It stands for
Ludwig Prandtl's deep humanitarian nature that together with the tough decisiveness ofsuch a consequent realism regarding conditio humana, he was all the same very soft tofellow human beings, full of consideration and kindness.''
In the winter-semester of 1946 Prandtl was made an emeritus. After that, at the age ofalmost 72, he retired as the Director of the Institute, with Professor Betz succeeding him.

169

However, it was considered necessary to create three divisions since the area that had
grown to be so vast in the meantime could not be handled by one single person. One
division was further on guided by Prandtl. Professor Tollmien who was called to succeed
Prandtl to the chair at the university, and Professor Betz were each responsible for one
division. Thus good co-operative work of this extraordinary team was assured.
Since Prandtl was now freed from a few duties, he could accept an invitation to go to
Switzerland in March 1947. Thanks to the initiative of Professor Ackeret in Zürich, theconditions necessary to realize the plan of undertaking this journey had been met.
Ackeret wrote to Prandtl on 30 January 1947:'Now I must actually write you once specifically about my efforts up so far, to enable you
and one of your daughters to spend a restful holiday in Switzerland.
Now, since the main problems of financing and permission by the Allies are settled, there
should not be any hurdles, in principle. In response to my inquiry, the three companies,
viz.
Brown Boveri Cie, Baden
Escher Wyss Maschinenfabriken
Gebrüder Sulzer, Winterthur
have expressed their willingness to shoulder gladly, the costs for a stay of about six
weeks for two persons. I wish to know now what special wishes you may have regarding
this stay.''
What it meant in 1947 to have, all of a sudden, the prospect of traveling to Switzerland issomething that can hardly be conveyed today. With the total shortage of goods of every
kind prevalent, one struggled relentlessly for the most elementary things, to maintainwhat was extant. In our imagination we could now picture the possibility of our living ina country that was spared from the ravages of war. In early March, my father could starton the journey and I was permitted to accompany him. Trains didn't run daily during
these post-war days, but only thrice a week. Finally, after many hours of journey and an
overnight stop in a bunker in Freiburg which had been improvised as a lodging, wereached the station at the border, Weil, where we were picked up. Some formalities had
to be attended to after which we boarded a train to Zürich. There we were sitting in ourworn out overcoats in a comfortable express train amidst Swiss who, in contrast to us,
were well clothed, bore an air of their natural self-assurance that we lacked, of course. A
few young people, returning after skiing, with red cheeks and sun-tanned, joked in amerry conversation. The war years that had been forced on us and the general depression
with the plight following it, had moved all thoughts on such pleasures of sport into a
distance, far out of reach for us.

170In Zürich we were very generously given a chance to improve the looks of our clothing.
We were put up in a very beautiful hotel. We thus enjoyed the extraordinary paradise-like
condition of being guests in unscathed Switzerland.
Professor Ackeret and his wife took attentive care of my father. Of course there was avisit to his Institut für Aerodynamik on the program; there followed a visit to the works ofGebrüder Sulzer in Winterthur and one to the workshops and laboratories of the plant
Escher Wyss. There was also a personal appointment made with Dr. H. Gygi whose
chauffeur brought us to his well kept private home in Wildegg where we spent a very
pleasant Sunday with his family. Herr Ing. Gygi, director of Maschinenfabrik Escher
Wyss was very much interested in discussing technical problems with my father. I
noticed, although being not able to follow the exchange of thoughts in content, how Dr.
Gygi thankfully acknowledged and agreed with the solutions suggested by my father.
I wish to mention here that I was very happy at that time to again meet my friend Lilli
Misch in Zürich who had migrated to Switzerland during the Hitler-dictatorship andcould study medicine there. She and her husband, Dr. Walter Baum, invited me and myfather to an unforgettable evening at the theatre in the Zürich Schauspielhaus: ''Der Tod
in Apfelbaum (Death in the Apple Tree)'' by P. Osborne was performed, with Albert
Bassermann in the leading role.
At the (Eidgenössische) Technische Hochschule, my father gave a lecture on turbulencein a colloquium. On 15 March, we traveled onward to Ascona on the lake Lago Maggiore
for a longer stay. These three weeks there were really restful for my father. We took
walks every day, regardless of the weather which was not very friendly. The view overthe lake in dull weather was charming again and again. On the return journey, in the
beginning of April, there were several items on the program that my father was keen on
doing. His interest in new projects and new publications in science had not decreased
with age.
In Weil am Rhein, he visited the scientists' group of Professors Schardin and Sauer, whowere engaged in building up a laboratory in the Elsass (in French: Alsacse) region. From
there, he traveled to Karlsruhe for a meeting in applied mathematics and physics, listened
to the majority of the numerous lectures, and didn't leave the discussions that followed.
After returning to Göttingen he himself noted: ''It was stimulating for me, but also
strenuous; and I have wasted a good part of my recovery again, but I still do not repent
having taken part in this meeting.''
On 3 July 1947, Professor Courant, coming from USA, visited the familiar old Göttingen.
In his diary he made a note: ''Arrived in Göttingen at seven-thirty in a bit of amelancholic mood. Outwardly, the town hardly shows any signs of destruction.
According to Karman, the town was explicitly excluded from the allied bombing raids.''
His diary entry regarding Prandtl: ''The Institut für Aerodynamik has been turned into areal fortress. Prandtl was sick and depressed, but still mentally very active. He had been
studying analog computers extensively, particularly for carrying out meteorological171

computations. The dimensions of the machine he designed were determined by the size ofthe ball bearing that he had found accidentally in war surplus goods.''
For the summer holidays, my father was invited to Ammerland by his brother-in-law,
Ludwig Föppl. This meant a rest in familiar surroundings, and, when needed, an
opportunity for exchange of scientific thoughts. In the beginning of July our second
daughter Susanne was born, and so naturally we stayed back in Göttingen.
Possibly it was during these holidays that Prandtl wrote this small article [36]:''On mammatus clouds:
I have observed this form of clouds quite often on my occasional holiday trips on theBavarian plateau. I concluded rather soon from the experiences of the related weather,that a threatening mass of cloud in which mammatus clouds are present, takes on apronouncedly harmless further course. Later, in an elongated mountain valley thatstretches itself in the north-eastern direction from the south-west end of the valley, I haveobserved there especially beautiful mammatus cloud formations out of a larger cloud
when the flow was towards south-west, and which moved rapidly down the valley. From
the overall form of the motion that had a certain similarity with the form of the motionthat appears in a liquid heated from below, it was entirely clear to me that there is an
instability present. It did not need much of further thinking to find out that obviously themass of air with clouds should be lying over a clear mass of air. The instability is createdby a downdraught within which the cloudy mass of air gets heated up more slowly thanthe clear mass of air. The fact that the flow was directed down the valley also provided,in this case, the explanation for the sinking as such.''These beginning lines of this article should suffice to gain an insight into how Prandtl
was stimulated to think in specific scientific terms through observations of a phenomenon
in nature.
In the meantime, new technically trained people were again recruited, and everyone, who
was taken on, regarded it as fortunate to have found employment there.
When Frau von Stutterheim related to me how she started working as a technical assistantwith Dr. Reichardt, she spoke with a deeply felt sympathy of ''the sympathetic oldProfessor Prandtl'' who came often to Dr. Reichardt's office. She had to undergo surgeryof the foot soon after beginning to work at her new job, and for a considerable length oftime could only walk with difficulty to her place of work. Prof. Prandtl, she said, showedvery much sympathy for her painful disability. He tried to cheer her up daily. Once, hetold her that he often counted his steps from home to the institute in order to ascertain if
the number of steps increased after some time had elapsed. Obviously he wanted tomonitor in this way, the aging that he accepted in advance.
There are similar thoughts that he expressed in a letter to Dr. A. Baeumker, given below.

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“To Dr. A. Baeumker, Fairfield, USA, 14 February 1949
I have still a long way to go, working on my book, before it comes to an end. I may
remark, in this context, that I am getting to feel my age in various respects. But there arestill ideas in plenty so that for a long time to come, I cannot think of writing my memoirs.
It is something my daughters would very much like to have. Herr Sommerfeld is now
over 80 and is writing a new book again. When I am that old, hopefully I will be able towrite down my memoirs, and, if that doesn't turn out to be so, that is nothing much to bepitied. Since, I see it myself in the young generation, that what interested us at our time is
no longer of interest to the younger people. Only when something existed long ago doesit start getting interesting.''
Excerpt from the letter of 1 June 1949:''Unfortunately, I have not understood much of your political discussion. Obviously I amvery poorly informed on matters political and can understand arguments relating to this
only when the matter concerned is told in clear and direct words.
I would also like to say that it is indeed quite interesting that my petition to Göring, inwhich I complained about the loathsome behavior of some national-socialist (NAZI-)
German physicists has been read in Wrightfield.''
Prandtl was now working, as has already been said, exclusively on meteorologicalproblems. He worked together with the meteorologist Dr. E. Kleinschmidt. His thoughts
and results appeared in a special issue in 1949 that was published by the Akademie derWissenschaften (Acadamy of Sciences). The introduction that is understandable to thegeneral reader is reproduced in the following. In the meantime, knowledge on this subject
has grown so stupendously that it appears rewarding to consciously recall the beginningsof this scientific approach through the said introductory passage.
Weather phenomena in the upper troposphere (presented at the meeting of 17 June 1949)[39]:''Forecast of bad weather regions (barometric low-pressure regions) along the Atlantic
coast of Europe was formerly a very difficult task, since these low-pressure regions
moved at a considerable speed from the sea to the land - apart from the main maritime
routes from where wireless messages come - and therefore could not be observed well intime before arriving on land. The introduction of radio-probes, that transmit to theterrestrial stations a report on the weather conditions prevailing well into the stratosphere,
and, with double exposure also furnish data on the strength and direction of winds in theupper regions, has enabled considerable progress to be made here. It has been discoveredthat in the high troposphere there exists even in the lower stratosphere layers, acharacteristic wind system with wind velocities up to over 100 m/s that travels ahead ofthe low pressure region. This announces the arrival of the low pressure region, so to say,whereby the wind velocity also indicates the strength of the low pressure region.

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Here, let a basic thought be mentioned that provides the requirement for the realcalculation, viz. that the air masses on the rotating earth drift alongwith the rotating
atmosphere.''The co-operation with the meteorologist, Dr. E. Kleinschmidt, led Prandtl to new
unsolved problems, which he addressed with verve and for which he found somecharacteristic solutions. Thanks to his richness in creative ideas, even in the subject of
meteorology, he could present significant results for publication.
At the Physicists' meeting on 6 September 1948, at which Prandtl was elected as an
Honorary Member of the German Physical Society (Deutsche Physikalische Gesellschaft)in the British Zone, he gave a small lecture on his way of working. Later, he was willingto put down on paper the thoughts he had expressed in the lecture, without the help ofwritten notes, in order to make the same accessible to a larger circle [31].
''I will gladly accede to the wish of Herr B., since up to now, I have refrained fromcomments upon the methods that have often enabled me to pursue new ways in myproblems. Especially since I believe I could give, in particular to the young colleagues,
useful hints through such remarks.
Herr Heisenberg, in his kind remarks of appreciation of myself, said that I have thecapability of ''seeing'' the solutions of equations without going through the calculations. I
must reply that I do not have this capability, but I strive to form in my mind a thoroughvisual intuition (Anschauung) of the ''things'' governing the problem on hand and to gain
an understanding of the phenomena. The equations come only later when I believe tohave understood the thing; they serve to get quantitative statements that cannot of course
be obtained by Anschauung alone. On the other hand, the equations are a good means ofproving my conclusions that others are ready to accept.''
Professor F. Schulz-Grunow, a former pupil of Prandtl, talked about this special starting
point in Prandtl's scientific thinking when he gave a lecture on the subject ''The
intellectual Heritage of Ludwig Prandtl'' (Das geistige Erbe Ludwig Prandtls) in October1980 [46]:''Prandtl first strove to understand the phenomena through Anschauung and gain a feel forthe differential equations. In the process of such feeling his way through, he found anumber of influences superposed on each other. He extracted the ones that matter, freed
himself of the inessentials, and saw that these were the ones that stood in the way of amathematical solution. A wonderful arrangement of nature was exposed to view. Prandtl
explains in is own words: Through a systematic simplification of the ansatz, that can betaken to different levels depending on the problem posed, a certain agility of the method
can be achieved. This turns out to be advantageous over the rigorous, but also rigid
method of the exact theory. Thus he created a new eminently successful dimension of
thinking.''
We return again to Prandtl's own speech:

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''The way of Anschauung mentioned earlier can indeed be learned, as I could see inseveral pupils.
In the old fashioned mathematics lessons that I went through around 1890 at high-school,
there were no functions, but only concrete individual examples. Therefore, in the firstsemester of study (at a university) it was a real eye-opening experience for me that there
are ''variables'' and ''functions'' of a variable. With a real craving, I plotted the different
functions y=x 'power' n for positive and negative n on chequered paper at that time. . . In
examples of mechanics I gradually got used to 'seeing' the forces and accelerations in theequations, or feeling with muscular sense, just as the stresses within the bodies under loadand so on...
Streamlines in two-dimensional flow could be regarded as lines of constant height of a'stream function', and through this a spatial model of this function could be visualized. So
there were various ways of making sketches of the solution sought. Such 'playing around'
led me, among other things, to the nice relation between shear stress distributions andsoap filaments.
Regarding the special tasks that I worked on, I got the idea from published works thatevoked a contradiction; but my failures, too, have made me reflect intensively.''
Let the example that follows illustrate this point: ''Shortly after 1900 hr. I came acrossseveral publications in which it was asserted that the exit velocity in a pressure driven jet
cannot exceed the speed of sound, although the energy is sufficient for reaching higher
velocities… The matter could be put into place easily. Euler's equations, together with thecontinuity equation for a compressible medium, yield stationary waves with supersonic
speeds [34]...''.
Still in the same month of September 1948, from 22nd to 24th, the first scientific meetingof the Society for Applied Mathematics and Mechanics (Gesellschaft für Angewandte
Mathematik und Mechanik, GAMM) in the British Zone was held in Göttingen. Prandtl,
who was the first chairman of GAMM since its founding in 1922, had successfully
negotiated with the Occupation authorities for grant of permission for re-registration of
the society. The British Scientific Adviser Dr. R. Frazer was interested. Prandtl had set
one lecture by himself on the program: ''Generation of circulation by shaking of vessels''.
He was also responsible for the course of the meeting. In this spirit he encouraged ayoung participant, Julius Rotta 1), to present a talk on a theme of his own. It was his firstlecture in public. One afternoon was planned for a walk of the party to Nikolausberg (ahill on the outskirts of Göttingen) where an informal round of talks was held over coffee
and cakes. The above mentioned participant (Julius Rotta)14 told me that the seventy threeyear old Prandtl was engaged in lively conversations with the conference guests.
Thereafter on the way back home, he led the group in vigorous strides to the mostbeautiful viewing points.
14

Dr. Julius Christian Rotta is the author of the book:''Die Aerodynamische Versuchsanstalt - ein
Werk Ludwig Prandtls, Ihre Geschichte von den Anfängen bis 1925'' [43].

175Even as an emeritus, Prandtl still kept the rhythm at work that he was used to. Besides
working on meteorological problems, he had undertaken to publish a new edition of his
book Strömungslehre to bring his text book up to the current stand.
He also participated in university matters that were discussed in meetings of the
Akademie. He also gave an address at the university celebrations held on 7 May 1949 on
the occasion of the hundredth birthday of the Göttingen scholar Felix Klein [26]. I will
quote from this address:''It might have been granted to me, as one of the 'younger people' to whom Felix Klein
became a destiny at that time, to talk from my memory about the experiences under his
leadership. It was the time when the gigantic undertaking of the Encyclopedia in
Mathematics (mathemathische Enzyklopädie) was launched under the leadership ofKlein. The fact that this work could be brought to a good finish really in accordance withhis original plans, goes to the credit of Klein alone who, through the inspiring influenceof his powerful, in fact kingly, personality, was in a position to spur the willing and theunwilling on to amazing performances.''
Perhaps the liberty can be taken here to quote from a letter of Prandtl written on 8 March
1949 to Professor Dr. A. Sommerfeld. It is about what a friend of Klein, Carl von Linde,
who became very well known for industrial liquefaction of air, had advised him at thattime when funds for starting an institute for technical physics were required, andfollowing that, for the project of a model laboratory (Modellversuchsanstalt):''If you,
Herr Klein, want to collect funds from industrialists, you will not scrap much together.
Something like this should be done in such a way that the richest of the industrialists is
won over for the cause first, and then one leaves him to do the fund collection. ...''
Von Linde then introduced him to the commercial director of the company Elberfelder
Farbenwerke, Henry Böttinger who was himself very keen on establishing close contact
with scientific circles. Thanks to his interest in Klein's ideas and his selfless personal
dedication for the big purpose, sufficient funds could finally be raised for technologicalresearch to be brought to the university. Thus, undoubtedly, he had a decisive share of
influence in realizing these new projects. Owing to Ministerialdirektor Althoff in Berlin
who worked in close co-operation with Klein, hereditary nobility was conferred upon
Böttinger and he was given a seat in the Prussian Hall.
1950 was the year of several jubilees, all concerned with Prandtl himself. He celebrated
his 75th birthday, the golden jubilee of his doctorate, 50 years of his membership ofVerein Deutscher Ingenieure (German Engineering Society), and in July 25 years of thehistory of the Institute, starting from Strömungsforschungsinstitut (the Flow ResearchInstitute) until the present post-war period.
Professor Tollmien wrote an article in the journal ''Forschungen und Fortschritte''(''Research and Development'') on the occasion of Prandtl's 75th birthday [49]. His career
is known to the reader, so I wish to quote here only the first and the last paragraphs from176

this article. Tollmien begins his article as follows: ''Epochs in the life history of a great
man do not keep in step with the number of years reaching a nice round figure. Such
predominant data are a reminder to the contemporaries to make sure what the merits ofthe celebrated are and preserve the achievements.'' He closes the article with thefollowing words: ''This brief survey of the work of Prandtl up to now should not obscure
his significant influence as a scientific educator. As the Göttingen institutes were built up
and expanded, a large number of Mitarbeiter joined the many doctoral candidates who
did their doctoral work with Prandtl in the course of years, and they benefited by his
stimulating suggestions in personal contacts. After becoming an emeritus in the year
1946, Prandtl, of course, stopped giving regular lectures, but he is actively engaged in
discussions in the colloquium over questions in applied mathematics and mechanics withthe richness of his superior knowledge and the temperament so characteristic of himself.
In the Max-Planck-Institut für Strömungsforschung Prandtl supervises research work as
the head of his own division. His publications of the last few years of which only a few
can be mentioned here go to show, not least, that Prandtl need not put on the robe of a'historic figure', but he is in the middle of a blessed, highly attractive creative old age.
May we all, Prandtl's pupils and friends, and colleagues in all the world, have the fortune
to see the man worthy of reverence live and work in our midst for long.''
He also received many congratulatory best wishes from his past pupils from foreigncountries too.

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27. The last years of life
In order to write about his last years of life, primarily on his activities and reflections ofseveral kinds, I have relied upon his correspondence during this time. But I will restrict
myself to writing only on such matters that refer to something entirely personal.
In his correspondence with earlier co-workers (Mitarbeiter) who had now found a new
sphere of activity in England, America, even Russia, the amicable relationship of mutual
trust that existed between Prandtl and his earlier pupils becomes clear again.
In his letter of 1 March 1950, Prandtl replies to the circular of Herr Professor Bock in
Moscow which had reached him. Professor G. Bock who was holding a leading positionin the laboratory Versuchsanstalt Adlerhof in Berlin since 1936, was taken prisoner at theend of the war and brought to the USSR. After a very tough time in Lubyanka-prison he
was permitted to do scientific work in the Aero-Hydrodynamic Central Institute in
Moscow. He suffered a great deal from the separation from his family.
From Prandtl's reply:''The circular gives a reasonably vivid picture of the kind of life you are leading there.
Unfortunately, it also says that you have become lonely by a working group going away.
Should this not change that soon, you will be conscious of your wife and children living
and of your taking care of the latter.
As far as I am concerned, I lost my wife almost 10 years ago, and although I have two
daughters, one of whom is childless and a war widow, the other with two daughters of 5
and 2 1/2 years and a lively young husband, this is no substitute for the wife with whom I
could share everything, my joy and my sorrow, for 31 years, and whom I have missedvery much since then. The saying that you quote in your letter, 'Getting used is given tous from above. It is a substitute for happiness' (Gewohnheit ist uns von oben gegeben. Sie
ist Ersatz fuer das Glueck), applies to me too. Under the present circumstances inGermany at present, where apartments are doubly occupied, due to destruction of housing
and Germans being driven out of the eastern countries, my daughters are living with me
and running the household. But that happiness was otherwise.
With the state of my health, I am quite contented, as far as one can demand of a 75 year
old.
The direction of work at the institute needed of course to be changed considerably fromthat of earlier times, and this is not yet completed. I myself still put in what I can, and I
have changed to working in my pet subject, which it was earlier too, viz. dynamic
meteorology. The science of meteorology is making big strides of progress, especially in
America, but also in Norway, Sweden and England, and appears to want to catch up withwhat has been lost up to now. Partly, it is also new research equipment like radar withwhich wind velocities can be followed in measurements even in high altitudes. Much is178known now about the atmosphere up to a height of 20 km so that it pays to follow theprocesses dynamically.
With this, I have embraced again in my old age a young science in which it is really apleasure to pursue things not researched hitherto. If this aspect of my work is looked at,
perhaps I am very fortunate again in matters of science!''
Even in a letter of reply that is really formal, he valued a very personal response:
16 December 1949: To The Indian Mathematical Society, Madras:''The Indian Mathematical Society has been so kind as to inform me that it is holding its
annual meeting from 26 through 29 December this year at the University in Madras. In
your invitation, you call me 'an eminent mathematician'. I can make no claims for thisdescription of myself. I am an engineer. If you want that way, a theoretician inengineering subjects, and I have used mathematics in the different cases of problems that
I have addressed. But I have never furthered the science of mathematics through any
contribution. I thank you very much for your good intentions and wish your meeting all
success.''
Our third daughter Ruth was born in April 1950, and, of course the grandfather was
happy to see the small grandchild growing up in his home again. But since then, I had
even less time to spend an evening chatting with Father. But my sister looked after his
welfare.
On the occasion of the Silver Jubilee of the Kaiser-Wilhelm-Institut für
Strömungsforschung (Kaiser Wilhelm Institute for fluid flow research) that was now
known as Max-Planck-Institut, a celebration was held in Göttingen on 15 July 1950
which was attended for the first time, after the war, by many earlier co-workers(Mitarbeiter) and pupils of Prandtl from home and abroad; it was also the last time when
he could gather together around him his older Mitarbeiter in larger numbers.
In late autumn, on 19 November 1950, a Saturday---it was my sister's birthday. As usual,
he took a walk through the woods. When, while bending down to pick up an ivy creeper,
he was suddenly hit by a stroke of the brain. He wanted to bring this unpretentious
ornament from the now monotonous autumn woods for decorating the table.
His own report on the incident is as follows: ''I did note something in my head, but withthe obstinacy that is mine I continued plucking.'' He came home limping. The doctor,
whom we immediately fetched diagnosed a paralysis of the leg and the arm, andprescribed absolute rest for him at home. For several weeks he remained our patient,sitting very patiently during the day in a broad reclining chair. But it is sad that his workat the institute had to be left lying unfinished. Visits from people who knew well how toentertain him and who kept him informed of the Institute affairs were stimulating andthey cheered him up. There is a letter dated 27 November to Herr Dr. Rotta that indicates
he was thinking of technical problems in spite of his weak physical state:

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''I have received a paper of S...for assessment…I have gone through the same frombeginning to end. When you have familiarized yourself with the contents and value of
Szablewski's work I would be happy if you would visit me in my sickroom.''
He could finally attend to some correspondence that had been left lying. There was one
matter of special urgency among them.
In a letter of 29 November 1950, Prandtl wrote to the Chair of the Catholic Church
declaring his intention to quit the Church. In this year Pope Pius XII had raised Mary's
Ascent to the Heavens to the level of a formal dogma.
''Delayed by pressure of work and finally by illness, I wish to declare herewith that I am
quitting the Church.
I learned from the newspapers that the mortal remains of the Mother Mary had beentransposed to the Heavens. This, as a fact of matter, is unimaginable for a person
educated in the sciences, and consequentially, cannot be prescribed as an article of faith
to someone who is pursuing the sciences with all seriousness. I wish to make the remarkthat I distanced myself inwardly from the Church already in 1905 when it concerned theanti-modernism vow.
Outwardly, however, I have kept my faith in the Church, since I have many precious
memories of youth that have kept me tied to the same. Whereas, at that time it was
gagging against the freedom of thought of Catholic priests, now it concerns my own
attitude.
I would be a dishonest person in my own eyes if, through my retaining membership of
the Catholic community, I would give my formal assent to the new doctrine which would
probably harm the Church much more.
It cannot stand the test of time if the Church continuously ignores the ideas of science...''
Visitors in the sickroom were, as already said, always very welcome. Once the painter
Wolfgang Willrich paid a visit. When my father learned from him in the course of theconversation that he plays the piano and had the habit of improvising freely at the
instrument, he requested him to open the piano and play. The powerful and pleasantsound of a musical creation of one's own soon filled the sickroom. My father was much
moved. I saw tears of emotion in his eyes. This way of making music in its naturalness
made him very happy. And the thought that since a few days he was not in a position toform a musical inspiration on the piano himself, might have made him painfully
conscious of his state.
How happy he always was to express his inside world through music. He thanked theguest profusely for playing, praised the talent of the guest who had so well succeeded indeveloping a charming musical theme, and contrasted his present failure.

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Herr Willrichs words of encouragement that he (Prandtl) should not give up hopes ofbetterment, however, sounded comforting. In fact, in the course of days of patient waiting
for betterment, there was some improvement. The paralysis receded gradually. As soon
as he could, he went to the Institute. In the beginning, he was picked up in a service car of
AVA, but soon he chose to be independent and started walking to the institute as everbefore. He was impelled to make progress at the work on the new edition of (his book on)
fluid flows. However, his energy for work had noticeably declined, and he got tired much
faster than before.
On 7 January 1951 he wrote to Professor Grammel:''The paralysis of my left leg has, in the meantime, receded quite substantially. I still limp
a bit, but I have started again to take short walks on Göttingen's Hainberg.''
On 19 January 1951 to Professor Busemann:''In the meantime I am going through the material for a new edition of my book andattending to what is new that has happened in the world.''
On 2 March 1951 to Professor Grammel:''I note with certain sadness that one is not allowed to get 76 years old unpunished, andregarding retirement, it has to be put off for later times.''
14 June 1951 to Professor G. Bock:''The reason for my replying only today is mainly that, of late, I have to work rather hardto prepare the new edition of Strömungslehre (Essentials of Fluid Dynamics). The pacewith which fluid dynamics is developing further, primarily through American
publications, has become so vehement that one cannot even think of giving an overview
of all the individual branches. My energy at work dwindles rather rapidly, and, inparticular, I am not at all in a position to really keep track of the current literature on thesubject. If I had foreseen this, I would probably have set my goals at a more modest level.
Since, from a 'guide' that this book aims to be, at the end of the day one expects that allthat is important should be mentioned. Already now, I take much help from my earlier
pupils, otherwise it would be a hopeless task. It is really a blessing for me that I do notunderstand Russian, otherwise the amount of material to be reviewed would be much
more voluminous… If the Russians want to change the state that their work is not being
known, they just have to prepare translations into a Western language, and they will
become known!''
In that spring of 1951, my husband procured a small car, a two-seater; but four people
could also sit inside. There were now some nice car-trips for my father, which he enjoyedhappily with us. Once, during a trip to the Harz mountains, when a shower of rain took us
by surprise, my husband noticed how, along the left edge of the windscreen considerable

181

quantities of rain water climbed up slowly instead of draining off. Since he liked to ask
questions, he drew my father's attention to this phenomenon. He (Prandtl) looked at it andsaid only one word stressing the same: ''Stimmt! (Yes, it is so!)''. One could discern thequiet smile conveying a certain humor with keeping distance at the same time, sincethrough this one word he was expressing satisfaction that the wet element takes a course
according to the rules 'prescribed' by the science of fluid flows.
For the summer of 1951, he had planned a longer period of vacation in order to relax
thoroughly. My sister accompanied him on this trip to Bavaria. This was his last summer
vacation.
On 10 November 1951 there was again a celebration of a jubilee in Göttingen: The
Academy of Sciences (Akademie der Wissenschaften) had been in existence for 200
years. It was founded in 1751, 14 years after Georgia Augusta (the university in
Göttingen). Teaching and research were supposed to be in a position to stimulate eachother this way. And as I have been told, it is certain that the 'Göttingen way' has been
influential in the shaping of modern institutions of higher education (Hochschule)elsewhere.
The President of the Federal Republic of Germany (Bundespräsident) Theodor Heuss hadcome to Göttingen on a visit for a few days on this occasion, which had set the whole
town in a happy mood. The then president of the Akademie der Wissenschaften Professor
Werner Heisenberg war the chairperson of this celebration. The grand ceremony took
place in the Aula on 10 November with many scholars from home and abroad attending.
On the day before this celebration, on 9 November, Heuss had honored the Max-PlanckInstitut für Strömungsforschung too by a visit together with the President of the MaxPlanck Gesellschaft, Otto Hahn. In a ceremony, he awarded Prandtl the Federal Medal of
Honor (Bundesverdienstkreuz).
Let me also give here one sentence cited from the speech Heuss gave in the Rathaus at
the end of his visit: ''Göttingen is a small city, but through it flow all rivers of the world.
(Göttingen ist eine kleine Stadt, durch die aber die Ströme der Welt gehen.)''For commemorating his visit the Bundespräsident planted in the presence of the entire
staff of the institutes there, a lime tree sapling on a circular flower bed close to the entry
gate. Since then it has grown to be a tall tree, and in well-informed circles it is referred toas ''Heuss-Linde'' even today.
The little that is still left for me to relate, before my father was hit by a second stroke inthe beginning of August 1952 is again the few personal notes on how he felt, that he used
to annex to his letters with technical content when he wrote to a friend and colleague.
22 April 1952 to Professor Blenk:

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''My own energy has, unfortunately, dwindled of late. So you shouldn't expect from me
any longer much of active involvement in this direction (he was elected to honorary
membership of the newly founded WGL - Wissenschaftliche Gesellschaft für Luftfahrt--Society for aeronautical science).
18 March 1952 to Professor Tietjens, Bangalore:''My own intention is to go to Bad Gastein with my daughter Hilde in order to cast all thesigns of aging into a milder form.''
On 1 May 1952 he traveled with my sister to Bad Gastein for three weeks. They were putup there in good quarters in the house of the emeritus colleague Pröll. However, thetreatments at the health resort put too heavy a strain on him, and on return he was not
feeling reposed. He was sad he had not been able to regain his earlier energy and stamina.
30 June 1952 to Dipl.-Ing. R. Langer, an earlier Mitarbeiter:''I cannot say things are going on well with me in all respects. I have decided, encouraged
by especially good experiences of colleagues, to undergo treatment at the health resort
Bad Gastein. But the healing baths have not improved the state of my health, so that I
now need to recover from the health treatment. So much is said of it in Gastein that thereal recovery starts a half year later. Let us hope for the best!''My father did not recover any longer from the sudden stroke of the brain that hit him in
the beginning of August. Infirmity returning led to a long period of confinement to thesick bed. We engaged a nurse at home. ''Schwester Lenchen'' was conscious of her special
duties and took care of her patient conscientiously and lovingly. She remained with us
until his death. How often have I heard her say: ''Herr Professor is so patient and modest,he has no wishes or demands. On the contrary he is happy with everything and thankfulfor every help, he is so considerate as to think on how he can make one or the other small
work easier for me. Never have I nursed a patient this modest and gentle.''The only embarrassment he caused to us in the beginning were his willful attempts to go
as usual to the Institute despite his weak physique. But having come there, his powers ofconcentration were absent. His tiredness could not be covered up, and he was broughtback home. Over all the years, AVA (Aerodynamische Versuchsanstalt) was at the realcentre of his life, and he got ready to part with it only with much hesitation and sadness atheart.
His medical condition got worse, and he knew that he would not recover any longer. He
resigned himself to the inevitable without complaint. On 15 August 1953 he died. Until
his last day he stayed in surroundings he was used to.
Difficulties cropped up at holding the funeral service for him, since the theologians of theuniversity denied to give a Christian prefatory note to a colleague who had quit the183Church. Without paying any regard to this fact, the vicar of the Reformed Church Pastor
Th. Kamlah gave the address at the grave. I will quote from this address.
20 August 1953:''Thoughts on the last and most profound questions of life he exchanged
with himself and usually did not talk over this matter. It was one of the most deeply
heartfelt hours in my professional life when he came to me on the death of his wife,
deeply touched, and allowed me a glimpse into his soft inner self.''
In his introduction to ''Collected Works of Ludwig Prandtl (Ludwig Prandtls Gesammelte
Abhandlungen), Prandtl's former pupil and later successor Professor Walter Tollmien
remembers [50]:''It was in November 1950 that he suffered a light stroke, from which, thanks not in theleast to the strength of his will-power, he soon recovered. But people around him
observed with concern the continuous dwindling of his strength a few months later. In
August 1952 the much feared breakdown happened after which he was no longer in aposition to express his thoughts in an orderly manner. Even then his benevolence at heart
shone through his behaviour. I was reminded of the aged Immanuel Kant who ended hislife in a similar way.
During my last visit to Prandtl, only his eyes spoke to me until he pressed my hand andsaid the two words:'Wir danken (We are gratelful)'. I know I will be acting in the spirit of
the immortalized if I pass on this thanks to all his Mitarbeiter (co-workers), to all those
who helped him at his work, and to his scientist friends.''184

28 Concluding remarks
Four years after Prandtl's death, an award bearing his name, to be given to
aerodynamicists of later generations, was instituted to honor Prandtl and to perpetuate thememory of his pioneering work in the aeronautical sciences. A golden ring, with hisname written in a highlighted script, was chosen as the symbol. It was given a name as
the LUDWIG-PRANDTL-Ring. The figure of an eagle which was to symbolize the spiritof freedom was engraved in a big stone of rock crystal.
The date for granting the award for the first time was chosen as 4 February, his birthday,of the year 1957. The Society for Aeronautical Sciences (Wissenschaftliche Gesellschaft
für Luftfahrt) gave this highest award to the aerodynamicist Theodore von Karman. Since
he could not be present in person at Göttingen, he sent a letter that was read at theceremony: ''I regard it as a great honor that I have been chosen to be the first recipient of
Ludwig-Prandtl-Ring… Prandtl's influence was decisive for my scientific development,
and I always remember him with gratitude and reverence.''
Since then the Ludwig-Prandtl-Ring has been awarded to many deserving
aerodynamicists who had worked with him previously as his pupils. They were scientistsof special eminence who had given new ideas for research (in this subject).
After the elapse of a hundred years since the birth of Ludwig Prandtl on 4 February 1975,
a memorial ceremony was held in the Stadthalle in Göttingen on 3 April (1975) by the
GAMM (Gesellschaft für Angewandte Mathematik und Mechanik) as a part of theirannual conference. Prandtl had been the first president of the GAMM for over 20 years[9]. The conference was also the platform for the Ludwig-Prandtl lecture. Here, which
was the 18th in the series, it was given by Fritz Schulz-Grunow. In the same year the
Max-Planck-Institut für Strömungsforschung brought out a Festschrift (commemerative
volume) on the occasion of its golden jubilee (50 years of existence) [18].

185Appendix
Prof. Dr. L. Prandtl
Annex to the letter of 28.IV.1941 - pp. 314/41 to Herr Reichsmarschall Hermann Göring
I. On theoretical physics
The goal of theoretical physics is to formulate a logically consistent structure of thought,
through which observed facts can be ordered within a framework such that even entities
lying far apart from each other may be explained in terms of a common basis, and with ashigh a degree of precision as possible. The laws resulting from this work may then serve
to predict new experimental results. A theory is required to be free of logicalinconsistencies, and its results should properly account for the facts. Depending upon the
hypotheses on which the theory is founded, there might be several valid theories for one
and the same set of observed facts. If a new event that is observed is in accordance with
one of these theories but not with the other, the latter should be discarded. This is the casethat arose around the turn of the century through what have come to be known as
Michelson's interference experiments. These experiments were expected, on the basis of
Newton's space-time concept that had been regarded as unquestionably correct until then,to provide conclusive evidence of the relative velocity of the earth with respect to theether in the universe. But, in spite of increasingly more sophisticated repetitions, theexperiments led to a negative result, i.e. instead of the expected shift in the interference
fringes there was no shift. With this finding, the Newtonian concept of space and time
proved to be basically flawed. H.A.Lorentz, in Leiden, was then able to show thatMaxwell's equations of electrodynamics do not lead to any inconsistency in the newexperimental observations, i.e. one does not run into inconsistencies if the observed
universe is regarded as made up of electrodynamic phenomena. It now became necessary
to reformulate, from a rigorous point of view, the space-time concept that satisfies thenew observations exactly. One such formulation was first advanced by A. Einstein. His
system is free of internal inconsistencies. It is, as already mentioned earlier, not the only
possible solution, but it is perhaps the simplest.
Vis-a-vis this issue of fact, the Lenard group buries its head in the sand like an ostrich,and holds steadfast to the Newtonian space-time concept, although this has been long
refuted by Michelson's experiment. The Einsteinian space-time concept, which has beenrecognized by clear thinking physicists from all over the world as the best solution today,
and which has become an indispensable foundation for further development of physics,
cannot, in the opinion of the Lenard group, be correct, simply because its creator was a
Jew. All further research studies, which have been conducted since then by Arischscientists on the basis of this new thought, are, in the eyes of the Lenard group, merely''Jewish physics'' (''jüdische Physik'' ).
The matter is somewhat different with quantum theory, which also started at the
beginning of the present century. The development of man's capacity for thought in186physics has taken place around the observable world. This, according to the establishedknowledge of today, consists of small particles (atoms), which are themselves made up of
still smaller elements. In all observable phenomena, even in the smallest region of space,
the number of such particles involved is still very large, and all phenomena seemed to fall
strictly into a cause and effect pattern, from which a causal principle was derived. The
entire body of earlier theoretical physics is built upon causal relations holding between
individual quantities. Today, with research probing into the inner structure of atoms, and,so to say, into the fundamental constituents of matter (the individual objects areperceivable separately through certain methods), it has been realized that the concept of
causality fails, and needs to be replaced by a statistical concept. (In the decay of radium
atoms, for example, there is no way of predicting when a certain radium atom is split. But
it is possible to make a statement concerning the fraction that disintegrates on average, in
one hour or a year, of a given amount of radium. Such statements are not restricted toradium, but are applicable to all atomic processes.) The causality of the older point ofview turns out to be the ''law of large numbers'', the ''law'' that arises when questions
concerning overall statistics, of every kind, are addressed. The larger the numbers, thesmaller the random deviations from the state that is to be expected from ''causal''considerations. The processes of energy conversion within the atoms, of which one has
no knowledge as to where and when an individual process occurs, also have the property
that, depending upon the type of conversion, only certain quanta of energy are converted
at a time (hence the name quantum theory). On the basis of such a point of view, it waspossible to hold a considerable number of earlier and recent facts of observation within
one logically consistent system. The Lenard people consider even this to be ''Jewish
physics'', perhaps according to the principle that I have heard mentioned now and then,viz. ''What I do not understand, I regard as Jewish''. Of course, there are contributions
from Jews to this part of scientific development, but the major share of contributions isby men like Planck and Sommerfeld to start with, all the way up to Heisenberg and
Schrödinger.
II. Details of the Lenard Circle
1. Lenard has earned much fame for himself through experimental investigations thatwould, in all likelihood, have led him to the discovery of X-rays, had Röntgen not got
there before. However, mathematical theory has never been his cup of tea, and it would
have been better if he had not started a controversy on mathematical subjects. In his oldage, he wrote a text book of many volumes, to which he gave the title '' Deutsche Physik ''(''German Physics''). The necessary clarity and rigour are absent in this book even when it
comes to the simple laws of ordinary mechanics, so it may pass as a text book forteaching at the lower level, but in no sense does it suffice for the higher level.
2. Another exponent of this group is Johannes Stark, the ex-president of the PhysikalischTechnische Reichsanstalt (Physics and Engineering Laboratory of the Reich). I know
Herr Stark from his days as a Privat-Dozent in Göttingen to be quite a passionate andeccentric person. Despite this, he is a superb experimentalist. He has two first-classdiscoveries to his credit, one of which, known as the ''Stark-effect'' in professional circles
all over the world, has made his name immortal. He has not, as far I know, engaged

187

himself with theory. But this has not prevented him from heaping abuse over and overagain on Herr Planck and Herr Heisenberg in unbelievably malicious articles, one ofwhich appeared a few years ago in '' Schwarzes Korps ''.
3. The group has a few followers, whose work is essentially of an experimental nature,
and whose contributions are invaluable that sense. But there are quite a number of people
who consider themselves to be unrecognized geniuses, but who, due to their poor
performance in the early days, could not make a mark; and they have poisoned the air
with that disdain for the past which is so fundamental to National-Socialism (Nazism).
Some in this circle engage themselves copiously in reforming the philosophicalfoundations of physics, and in particular the space-time concept. For all these people, theMichelson experiment is of no consequence whatsoever in this venture; or in other words,
they stick to the Newtonian space-time concept. 15
4. Choosing a successor to the world-renowned Munich theoretician Sommerfeld---towhom, besides many other things, one owes a clear ordering of the laws of spectral lines is something special. This successor, Wilhelm Müller, was earlier an Assistent, and later
became a professor of technical mechanics, first in Hannover, later in Prague andAachen. Until now he has worked primarily on fluid flows and flight mechanics, and has
also written text books on areas of these subjects. He possesses no qualifications intheoretical physics, absolutely none. Instead of giving lectures on subjects needed in the
education of physicists, viz. electrodynamics, electron theory, optics and radiation,
thermodynamics, mathematical statistics and partial differential equations of physics, helectures, according to his own statements, on flight mechanics and other branches ofengineering mechanics. It cannot be denied that it is useful, even for those attending auniversity, to get to know something of these subjects. But, if, on this account, they areleft unexposed to an essential part of physics, it generates a state that can only bedescribed as a sabotage of essential teaching. Herr Müller has expressed himself
extensively on his programme in the journal ''Zeitschrift für die gesamte
Naturwissenschaft '' (November-December 1940, pp. 281-298). In this article bearing
the title ''The State of Theoretical Physics in the Universities (''Die Lage dertheoretischen Physik an den Universitäten''), he has not failed to pass adverse comments
concerning the German representatives of theoretical physics. As far as the rest areconcerned, the Lenard Group is profuse in its profession of a faith in physics: the article
suggests that, among the theoreticians, there is a ''secret group of authorities' ' forcing
people… ''almost by magic, to subscribe to a certain program'' that ''threatens everyone
who ventures to express an opinion of his own independent of the Guild''. (I wish to notehere that the ''secret authorities'' are none other than the experimentally observed facts,
and the threats to those thinking otherwise are nothing but the justified rebuttal of those
who do not want to see the facts.) Incidentally, the publisher Helingsche Verlagsanstalt
in Leipzig has announced the publication of a brochure under the title ''Jewish andGerman Physics'' (Jüdische und deutsche Physik) authored by Herr Stark and Herr15

See different, partly malicious articles by Kubach, Thüring, Dingler and others in the journal''Zeitschrift für die gesamte Naturwissenschaft '', a journal that proclaims itself in its sub-title as''The voice of the Reichsfachgruppe Naturwissenschaft der Reichsstudentenführung ''. (There is alist of editors on the inside of the cover page,)188

Müller, which promises a fierce campaign ''against a dogmatism that still clings on to theJewish spirit, that does not serve truth and knowledge, but pursues the goal of assaulting
nature and degrading it to be a mere servant of formulas''. The brochure is supposed to
explain, through examples , ''the basic difference between this Jewish or Jewishinfluenced theoretical arbitrariness and the German pragmatic theory'', noting that thelatter ''does not aim at establishing that everything observable can be traced back to agiven order that is easy to visualize and understand through a system of laws of
causality.''
I believe that these sample extracts from their texts suffice to characterize the attitude of
the Lenard group adequately.
L. Prandtl

189

At his working desk

190

Literature cited[1] Ackeret, J., Das Rotorschiff und seine physikalischen Grundlagen. Verlag
Vandenhoeck & Ruprecht, Göttingen 1925
[2] Ackeret, J., Ludwig Prandtl siebzigjärig. Neue Zürcher Zeitung, 166 Jg, Sonntag 4.
Febr. 1945
[3] Betz, A., Aus der Geschichte der Aerodynamischen Versuchsanstalt Göttingen. Jahrb.
1957 d. Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V., pp. 40-59[4] Betz, A., Das Lebenswerk von L. Prandtl. Neue Zürcher Zeitung Nr. 1953, 11. August
1954[5] Betz, A., Die AVA und das Max-Planck-Institut für Strömungsforschung. Mit einer
Ergänzung von L. Prandtl. In: Die Geschichte der KWG und MPG 1945-1949. Aus
Anlass d. 70. Geburtstages ihres Präsidenten, Otto Hahn, 6.3.1949, pp. 20-40[6]Betz, A., Ludwig Prandtl zum 70. Geburtstag. Forschungen und Fortschritte 21/23,
1947, p. 31[7] Beyerchen, A. D., Wissenschaftler unter Hitler. Title of original edition: Scientists
under Hitler, Yale University 1977. German translation by Erica and Peter Fischer,
Verlag Kiepenheuer und Witsch, Köln 1980
[8] Föppl, O., Windkräfte an ebenen und gewölbten Platten. Jahrb. d. MotorluftschiffStudiengesellschaft 4, 1910-1911, Verlag J. Springer, Berlin 1911, pp. 51-119[9] Gedächtnisveranstaltung für Ludwig Prandtl aus Anlass seines 100. Geburtstags,
verbunden mit der 18. Ludwig-Prandtl-Gedächtnis-Vorlesung. Zeitschr. f. Flugwiss., 23,
1975, pp. 149-183[10] Göttingen unterm Hakenkreuz. Stadt Göttingen, Kulturdezernat 1983[11] Göttingen 1945, Kriegsende und Neubeginn. Stadt Göttingen, Kulturdezernat 1985
[12] Heisenberg, E., Das politische Leben eines Unpolitischen, Erinnerungen an Werner
Heisenberg. R. Piper & Co. Verlag, München, Zürich 1980
[13] Hergesell, H., Prandtl, L., Das Projekt einer Reichsversuchsanstalt für Luftschiffahrt.
Jahrb. Dtsch. Versuchsanst. Luftf. Bd1, 1912/13, Verlag G. Stilke, Berlin, pp. 39-52 (In[50]: p. 1412)[14] v. Karman, Th., Aerodynamik, Ausgewählte Themen im Lichte der historischen
Entwicklung, Interavia Genf 1956. Original edition: Aerodynamics: Selected Topics inLight of Their Historical Development. Cornell University Press 1954

191

[15] v. Karman, Th. with Lee Edson, Die Wirbelstrasse. Hoffmann und Campe Verlag,
Hamburg 1968. Original edition: Original edition: The Wind and Beyond. Little, Brown
and Company, Boston and Toironto, 1967
[16] v. Karman, Th., Ludwig Prandtl. Zeitschr. Flugt. und Motorl. 16, 1925, pp. 37-39[17] Kraemer, K., Geschichte der Gründung
Strömungsforschung in Göttingen, In [18]: pp. 16-34

des

Max-Planck-Instituts

für[18] Max-Planck-Institut für Strömungsforschung in Göttingen, 1925-1975. Festschrift
zum 50-jährigen Bestehen des Instituts. Hrsg. MPI f. Strömungsforschung Göttingen,
Hubert & Co.. Göttingen 1975[19] N.N., Ludwig Prandtl 70 Jahre. Luftfahrt-Forschung 21, Febr. 1945, Lfg 2, pp. 1-3[20] Prandtl, L., Anwendung der turbulenten Reibungsgesetze auf atmosphärische
Strömungen. Proc. IV Intern. Congress Appl. Mech., Cambridge/England 1934, pp. 238239 (In [50]: p. 1098)[21] Prandtl, L., Bemerkungen über den Segelflug. Zeitschr. Flugt. Motorl. 12, 1921, pp.
209-211 (In [50]: p. 520)
[22] Prandtl, L., Der Lutwiderstand von Kugeln. Nachr. d. Ges. d. Wiss. zu Göttingen,Math.-phys. Kl., 1914, pp. 177-190 (In [50]: p. 597)[23] Prandtl, L., Die Aerodynamische Versuchsanstalt der Kaiser-Wilhelm-Gesellschaft
und ihre Bedeutung für die Technik. Die Naturwissenschaften 10, 1922, pp. 169-176 (In[50]: p. 1294)[24] Prandtl, L., Eine neue Darstellung von Torsionsspannungen bei prismatischen
Stäben von beliebigem Querschnitt. Jahresber. Math. Ver., 13, 1904, pp. 31-36 (In [50]:p. 81)[25] Prandtl, L., Erste Erfahrungen mit dem rotierenden Laboratorium. Die
Naturwissenschaften 14, 1926, pp. 425-427 (In [50]: p. 1304)[26] Prandtl, L., Felix Klein und die Anwendungen der Mathematik. Universitätsbund
Göttingen e. V., Mitteilungen, 26, 1949, H.1, pp. 7-11[27] Prandtl, L., Führer durch die Strömungslehre. Verlag F. Vieweg & Sohn,
Braunschweig 1942 (2 further editions revised by Prandtl appeared in 1944 and 1949; thelatter was reprinted without change in 1956 and 1957 to meet the high demand. K.
Oswatitsch and K. Wieghardt brought out 4 new editions between 1956 and 1990, towhich further authors have contributed, All together, 9 editions of the book haveappeared)192

[28] Prandtl, L., Kipp-Erscheinungen. Ein Fall von instabilem elastischem
Gleichgewicht. Inagural Dissertation d. Phil. Fakultät, Sekt. IId. Ludwig-MaximiliansUniversität München 1899 (In [50]: p. 10)[29] Prandtl, L., Lehren des Röhnflugs 1922. Zeitschr. Flugt. Motorl. 13, 1922, pp. 274275 (In [50]: p. 526)
[30] Prandtl, L., Magnuseffekt und Windkraftschiff. Die Naturwissenschaften 13, 1925,
pp. 93-108 (In [50]: p. 1503)[31] Prandtl, L., Mein Weg zu hydrodynamischen Theorien. Phys. Blätter 4, 1948, pp.
89-92 (In [50]: p. 1604)[32] Prandtl, L., The generation of Vortices in Fluids of Small Viscosity. Jo. Roy. AeronSoc., 31, 1927, pp. 720-743 (In [50]: p. 752)
[33] Prandtl, L., Tragflügeltheorie I. Mitteilg. Nachr. d. Ges. d. Wiss. Göttingen, Math.phys. Kl., 1918, pp. 151-177 (In [50]: p. 322)
[34] Prandtl, L., Über die stationären Wellen in einem Gasstrahl. Phys. Z. 5, 1904, pp.
599-601 (In [50]: p. 891)
[35] Prandtl, L., Über Flüssigkeitsbewegung bei sehr kleiner Reibung. Verhandlungen d.
III. Internat. Math. Kongr. Heidelberg, 8.-13. Aug. 1904, B. G. Teubner, Leipzig 1905,
pp. 485-491 (In [50]: p. 575)
[36] Prandtl, L., Über Mammatuswolken. Ann. Meteor. 3, 1950, pp. 119-120 (In [50]: p.
1179)[37] Prandtl, L., Verhandlungen der Versammlung von Vertretern der Flugwissenschaft
am 03. bis 05. Nov. 1911 zu Göttingen. Verlag R. Oldenbourg, München und Berlin 1912
[38] Prandtl, L., Vorträge an der Kaiserl. Universität in Tokio: Über Turbulenz, J. aeron.
Res.Institut, Tokyo Imp.. Univ., 5, No. 65, 1930 pp. 12-24 (In [50]: p. 788). ÜberGasdynamik, ibid., pp. 25-34 (In [50]: p. 998). On the Role of Turbulence in TechnicalHydrodynamics. World Eng. Congr. Tokyo 1929. Proc. Tokyo, 5, 1931, pp. 495-507 (In[50]: p. 798).
[39] Prandtl, L., Wettervorgänge in der oberen Troposphäre. Nachr. Akad. Wiss.
Göttingen, Math.-phys. Kl., 1949, pp. 13-18 (In [50]: p. 1173)[40] Prandtl, L., Zur Torsion von prismatischen Stäben. Phys. Zeitschr. 4, 1903, p. 758(In [50]: p. 79)

193

[41] Prandtl, L., Zur Vorgeschichte der Wissenschaftlichen Gesellschaft für Luftfahrt.
Zeitschr. Flugt. Motorl. 13, 1922, pp. 156-157 (In [50]: p. 1497)[42] Reid, C., Courant in Göttingen and New York. Springer Verlag Berlin, Heidelberg,
New York 1979[43] Rotta, J. C., Die Aerodynamische Versuchsanstalt in Göttingen, ein Werk Ludwig
Prandtls. Verlag Vandenberg & Ruprecht, Göttingen 1990
[44] Runge, I., Carl Runge und sein wissenschaftliches Werk. Vandenberg & Ruprecht,
Göttingen 1949
[45] Schaefer, H., Erkenntnisse und Bekenntnisse eines Wissenschaftlers. Verlag fürMedizin Dr. Ewald Fischer GmbH, Heidelberg 1986[46] Schulz-Grunow, F., Das geistige Erbe Ludwig Prandtls. Jahrb. 1980 d. Deutsch. Ges.
f. Luft- und Raumfahrt, pp. 37-9 to 37-27[47] Staatsbibliothek Berlin (Hrsg), Max Born, James Franck, Physiker in ihrer Zeit. Der
Luxus des Gewissens. Ausstellungsexemplar, Stiftung Preussischer Kulturbesitz Berlin
1982[48] Stamer, F., Zwölf Jahre Wasserkuppe. Hobbing Berlin 1933[49]Tollmien, W., Ludwig Prandtl zum 75. Geburtstage. Forschungen und Fortschritte
26, 1950, pp. 103-105[50] Tollmien, W., Schlichting, H, Görtler, H. (Hrsg), Ludwig Prandtl. Gesammelte
Abhandlungen zur angewandten Mechanik, Hydro- und Aerodynamik, 3 Bde. SpringerVerlag Berlin, Göttingen, Heidelberg 1961
[51] Willers, Fr. A. (Hrsg), Festschrift zu Prandtls 70. Geburtstag, Zeitschr. Angew.
Math. Mech. 24, 1944, pp. 185-300

194Glossary
During translation, it became clear, as might have been expected, that the meaning of theoriginal, as intended by the author, is better preserved by taking over the German word
into English instead of another choice, say according to a dictionary. The main guideline
adopted for translation has been conveying the meaning intended by the author, and in
this spirit, German words have been taken over wherever this is, in the opinion of thetranslator, more appropriate. When this has been done, the German word has been set initalics. Its meaning, although often self-explanatory, is given in brackets to facilitate
understanding. The following Glossary lists a selection of these words that occur more
often, together with a brief note on its meaning in the context of its use.
Aktuar civil servant in the Department of JusticeAmtsrichter district court judge
Arisch one finds this word often translated as 'aryan'. The roots of this word, as areference to a standard dictionary, e.g.. Oxford Illustrated (1984), Webster's New
Dictionary (1995), or Chambers's Twentieth Century (1964), would show, can be traced
back to Sanskrit. Its meaning, in the dictionary, is 'noble', and it is in this meaning that theword 'aryan' has been used in the abundant literature in Sanskrit and other Indian
languages, both old and recent, as well as in literature on Indian languages and culture in
English, German and other European languages . However, the meaning this term has
acquired after its use by the NAZIs to designate the 'aryan' race, mostly in the context ofstanding out against the 'Jewish', has been exactly the opposite. A discussion on themeaning of the word 'aryan' as such does not fall within the scope of the present
translation, but, in order to convey the meaning of the term as used in the context more
properly, the translator has opted to take over the word 'arisch' unchanged.
Assistent an assistant attached to an Ordinariat. An Assistent was entrusted with carryingout duties at a higher level, both of scientific and organisational nature, than those done
commonly to an assistant in English or American universities, or other universities
following this tradition
Auskippen deflect away, lateral deflection
ausserordentlicher Professor professor without a chair, in the days of Prandtl without
voting rights in the Fakultät
AVA abbreviation for Aerodynamische Versuchsanstalt, Laboratory for aerodynamic
testing
Baurat building councillor, designation of a civil servant in the public works department
Diplom-Ingenieur title awarded on graduation in engineering at a technical university(Technische Hochschule)195

Dozent a person entitled or commisioned to teach at a Hochschule, as an Ordinarius,auserordentlicher Professor, or a Privat-Dozent
Extraordinariat position of an ausserordentlicher Professor
Fakultät an autonomously governing unit in academic matters in German universities
Gau the word is an old German word for an area surrounded by water (not necessarily an
island) or, later, a settlement. There are many old towns and areas in the German
speaking parts of Europe whose names end with gau and their meaning is easily
understandable in this context. The word was also used to designate an area under thejurisdiction of a court. and/or an administrative district. It is no longer employed in thismeaning after 1945
Gauleiter official (mostly of the Party NSDAP) entrusted in charge of the Gau, in a
powerful position
GAMM- Gesellschaft für Angewandte Mathematik und Mechanik (German Society ofApplied Mathematics and Mechanics, founded by L. Prandtl and R. Von Mises
Geheimrat title awarded by the King or the Kaiser (until 1918) , roughly equivalent toPrivy Councillor
Habilitation the process of earning a Venia legendi at a university
Hilfsassistent an auxiliary assistant, a helper assistantHilfskraft, Hilfskräfte (plural) helping hands
Hochschule an institution of higher education, can refer to both, a college or a university
Institut a research unit within the Fakultät, generally headed by an Ordinarius
Ith the Ith is the crest of a hill along the river Weser near the town of Hameln, known tomany from the 'Pied Piper's' story
Keplerbund club of scientists that had given itself the name of the great astronomer
Kreis an administrative unit smaller than the Gau
Kurator Trustee
KWG abbreviation for Kaiser-Wilhelm-Gesellschaft, forerunner of the present MaxPlanck-Gesellschaft (MPG)

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Luftwirbel vortices in air. There is a pun in the use of this word in the present context(Chapter 3) which would amount to the same as 'making a lot of (empty) noise'
Ministerialrat designation of a senior civil servant in the ministry
Mitarbeiter literally, a co-worker. The word is often used to designate one in asubordinate position, not in a supervisory or managerial position
Modellversuchsanstalt Laboratory for Model Testing
Motorluftschiff-Studiengesellschaft Society for the study of Powered Airships
MPG abbreviation for Max-Planck-Gesellschaft. MPG
NSDAP abbreviation for Nationalsozialistische Deutsche Arbeiterpartei, the Party of the
NAZIs
Oberamtsrichter Chief District Judge
Ordinariat chair of an Ordinarius. An Ordinariat was equipped budgetarily, with acertain number of Assistents, secretarial staff, Mitarbeiter and (technical) personnel, as
needed, often negotiated as terms of appointment
Ordinarius a full professor, with a chair, at a university. Generally, the head of an Institut
Privat-Dozent a person entitled to teach at a university, one having a Venia legendi. For
an explanation from a humorous angle the reader may wish to see reference [15], p. 45
Promotion the process of earning a doctor's degree at a university through writing a
Dissertation
SS-Hauptmann holder of the rank of a Captain in the SS
Steuerliquidator civil servant in the Ministry of FinanceVerein Deutscher Ingenieure (VDI) German Society of Engineers
Venia legendi the right to teach at a universty. It is granted by the Fakultät, it is to beearned by presentation of a thesis
Weltanschauung view of life, used with a philosophical touch
Zeitschrift des Vereins Deutscher Ingenieure (Fachgruppe Luftfahrt) Journal of VDI(aeronautics division)

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