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Copenhagen,Blegdamsvej 15. 5/12 1928
Dear Dr. Nishina
Thanks very much for your two kind letters.

I was glad to hearthat you have had a good journey to America. I hope the four weeks in
America have been a good and interesting time for you.

Just to‑day I

think you are starting for Japan; don t you look forward to see your own
country and your friends there again?
Here everything is as usual; we have still Garnow, Mott and Hartree
here; Hartree and Mott will leave in a week I think. Professor Bohr is
so occupied by speaking with them every day, so he cannot get time to do
his own work in the daytime; therefore we sometimes work in theevenings, last saturday I worked till half past eleven p.
m.

To‑morrow

there shall be a Doktordisputats， （Mr. H￠jendahl) and Professor Bohr
shall be Opponent （ excuse me using danish words, but I don't know what
it is called in English). But you have not forgotten the Danish
language yet, I suppose! It is really a long time you have stayed here,
but I have been at the institute for 9 years now, it is dreadful tothink of, how quickly all these years have flown and how old one hasgrown.
Mrs. Bohr told me the other day,that Professor Hevesy has got ason. The baby‑Bohr is sti11 i11, I don t think he is improving a bit,poor little fellow.

Do you see Mr. Kimura and Takamine, and perhaps

also Sugiura,Hori and Aoyama? If you see them, please, give them mykindest regards.

Now we have soon Christmas again, you have no

Christmas in Japan, have you? If you have a little time to write andtell me about your getting on in Japan, I shall be very glad indeed.
I send you the very best wishes for the new year and hope you will

2

be in good health and good spirit; the kindest regards from
i

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Institute of Physical and

6th April, 1929Chemical Research
Komagome, Hongo, Tokyo
Dear Professor Bohr,At the time when you receive this letter, you are, I suppose, inthe middle of the Danish spring, which 工 used to enjoy very much andwhich I can visualize vividly.
Here we shall have cherry‑blossoms in their full beauty in a weekor ten days. In just a year we expect to welcome you here and hope you
will enjoy our spring・

We are very often speaking about your coming

over here. One of the newspapers in Tokyo has written about it already.
Professor Nagaoka is taking care about the arrangements,he asked me theother day whether you could stay longer than one month. We all wish
that you could stay as long as possible. Professor Nagaoka expects to（＊｝obtain ten thousand yen
for your stay, although it has not yet been
decided definitely as I have understood it.

As soon as your plan isfixed, please let me know.
I am having a quite satisfactory life after marriage, but themarriage has had its consequences which have taken whole my time sincethen: All sorts of formalities,arrangements, family affairs and so on.
I have thus been unable to do any physics at al1, but hope soon to get
into a serious work again.

3

I am sending you a small cigarette‑box by parcel post. This is
Just to express my thanks for your kindness which you extended to me inall respects regarding my scientific as well as personal life while I
was in Copenhagen.

I should be only too pleased, if you would

acknowledge the feeling of my gratitude through it. This will come toyou certainly much later than this letter as they send the parcel post
via Canada.
Takamine and Sugiura are in this Institute and Kimura in the
University here. Owing to illness, Takamine has been absent from theInstitute for about a month, but has now recovered and will soon begin
his work again. Sugiura is calculating as usual and Kimura continuing
his work in Copenhagen. Just a day ago Aoyama appeared in Tokyo. He is
working at Sendai, he will set up a laboratory for low temperatureinvestigation.
Whenever we meet to‑gether, our conversation never end without
coming to Copenhagen, which we all miss very much, especially I miss
F lledparken and Langelinie, the parallel of which we have not in theneighbourhood of our Institute, so that I could take a nice walk when I
get tired of my work.
With kindest remembrances and best wishes to all of your family andyourself, and all in your Institute too,

v
a

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s

One yen is two shillings at par, but it is about
10も belowpar at present.

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4

Kφbenhavn
April 10. 1929

Jtp
rべ 0 ・ 1
'ユ1
・
／

／

Um Ihren Eindruck vollstandig zu machen, schreibe ich 泣 き 戸 ￡ 品 号 士 官T
(falsch) deutshch.

Wir haben hier eine wu.
nderbare Physikerkonferenz,

bei der alle ‑besonders ich
一
一 Gelegenheit haben Ihre spezifischen
Unarten zur Schau zu stellen.

Schade dass Sie nicht hier sind. Sie

M.tten Ihre belle Freude davon! ‑ Heute Abend bei Klein ich ein wenig
Gelegenheitfiir mich,

meine

stark

vernachlassigten menschlichen

Qualitaten zu pflegen. Dies ist nur dadurch sehr erschwert, dass die5Leute mich immer erziehen wollen!

Herzliche Grusse
W.Pauli

April 10, 1929
Dear Nishina,
This little group of your old friends wishes to send you greetingsfrom this country where you have been so long・Gerda and I and thechildren talk often of you and hope that in not too distant a future weshall see you here again. Thank you for your long letter. I shall soon
write you again.
Many good wishes for the futureYours,
Oskar Klein

The picture is made by Rosseland. Many greetings fromme also, wewill miss you this summer in the country. Probably we will go to thewestcoast of Jylland together with my family.
Best wishes.
Yours,
Gerda Klein

6

Dear Nishina.
We are on a short trip to Copenhagen, occasioned by a physicalconference at the Institute.

we are glad to send you our best

greetings, and wish you many happy days in Japan.

'
l
'
h
a
n
k you for yourkind greeting fromMount Wilson
Yours sincerely
S.Rosseland

Dear Nishina:
What are you doing these days?

Have you already improved Japan?

We are jointly enjoying the many advantages of Copenhagen, with which
you are well familiar. Good luck 4, 3, 2, 1 now!
KronigViele herzliche Grusse！ 日offentlich sehen wir uns bald einmal
wieder!
P.JordanBlegdamsvej 15, April 30 1929
Dear Dr. Nishina!
Thank you very very much for your most kind and interesting letter
which I was so glad to receive a fortnight ago, and thanks also for the
lovely book‑mark you were so kind to send me. And 工 must send you theheartiest congratulations and best wishes for your marriage． 工ndeed, I
was surprised when I heard that you had married and have thought so much

7of you. It must be strange to be married to a person of whom one does
not know much and before love has come, but I really hope you have had agood luck and have got a good and sweet wife. Don t you find it nice tohave got your own home? It is a good thing that you have not found it
so difficult to accustom yourself to the Japanese conditions again,
which surely must be most different from those in Europe.
Believe me, we are all missing you very much here at the instituteand speak often of you.

Three weeks ago here has been a smal1

conference of most of the physicists who have been working here the lastyears.

Some of them had written and announced their visits in the

Easter holidays and this gave Professor Bohr the idea of the conference.
Prof.Kramers was here, and Ehrenfest, Pauli, Jordan, Kronig, Darwin,
Holtsmark, Heitler, Nordheim, Mott, Rosseland and others. Gamow is
still here, but now he will leave us in a few days. Dr.Trumpy from
Tronhjem is here for 5 months and Dr. Hiickel from Zurich is here for 3
months, both of them have their wife and a baby with them. It was avery busy time for Prof.Bohr during the conference, there were lectures
every day during the week at 10 in the morning to 12, and then from 2
0・clock to 5‑6 in the afternoon. Prof. Bohr opened the conference

himself the first day, and thereafter there were lectures by Gamow,
Heitler, Pauli, Klein, Darwin and Kronig.

Dr. Fues, Waller and theGoudsmits were also here. The first evening they were here we were all
invited to Prof. Bohr in the evening and the last day after the
conference, it was Sunday the 14. April, we had an awfully niceexcursion in two

Turist‑Biler.

We started from the institute at 9 30

and went to Hiller￠d, where we looked at Frederiksborg on the outside,
there was not time enough to go in, then to Tisvilde where we got lunch
in Professor Bohr s house and walked

through 'l'isvilde

Hegn

toBrantekjerg and then along the shore to '
l
'
i
s
v
ildeleje. I walked some of
the time with Kronig and he spoke about the time where you and he were
living in Tisvilde.

Then we had a beautiful drive through Raageleje

Gilleleje Hornbock and Helsing￠r and then back to Copenhagen.

It was avery nice day and indeed the only real spring‑day we have yet had. It
has been a very severe winter and even now at the end of April we have8

still snow weather.

I am sure it is better in Japan, the cherry

blossoms must be lovely. How is your house?

Is it a stone‑house andfurnitured like the houses here or not? 一Prof.Bohr is getting on well
but he looks a little old 工 think,he is as usual working too much, but
he is just as kind as he has always been, he is never angry always
amiable, even if one does something foolish. Mrs Bohr s baby has comein a hospital now,he is still ill, can neither go nor say anything.
Do you think you will come back here in 2‑3 years as you had
thought of or will your marriage make alterations in your plans? Wehave had a young Chinese here for a few weeks.

Dr.Chou, it is thefirst Chinese here has ever been. He was very nice, has now gone backto China, but thought of coming back in 2 years.

There was taken aphotograph of the conference gentlemen in the auditorium. I shall send
you a copy, it may perhaps amuse you to see the old acquaintances.
I understand so well that you are very busy, and 工 can think thatyou have a lot of friends to write to, but I should be so glad to hear alittle from you sometimes, when you have a little time left. A
new‑year's time I got a greeting from Mr. Kimura, it was very kind of
him to remember me. Is he still quite well?
I am getting on well myself 一the spirit is not always so good, ‑but never mind. I hope you are well and that you will be really happy.
The kindest remembrances and best wishes
Yours very sincerely
Betty Schultz

9

Meilguard 20. 7. 1929
Dear Nishina,
I am very much ashamed that I have not yet thanked you for yourlong nice letter, which we were so glad to receive, and for the
beautiful box you sent us. It was much too kind of you to send us thisbeautiful gift, which together with the other things you hav.
e given us
we shall keep as a remembrance of you. We are often talking of you andoften missing you especially here in the country where we are remindedof last summer. I for my part do not least miss our discussions about
scientific and other matters which have signified more for me than you
may know.
We are now hoping that you will be much more happy in your homethan you dared to think when you left Denmark. From your last letter webelieve that this hope is not unfounded. We are very eager to hear fromyou, both about your life and your work.
This summer we are staying at Meilguard at the coast of Jylland
together with my wife s family, which are all sending you many
greetings.

This is a very pretty place and quite as genuine country as

Lundeborg and with better shore, so that we all enjoy the bathing.
From the laboratory there is not so much to tell.

When I left,

Bohr had just finished a small article of rather philosophical content
for the Planck‑Heft of Naturwissenschaften, which, I think, willinterest you. I hope the reprints will soon arrive.一 We had a shortvisit of the Rosselands one of the last days of May.

They had been in

Gottingen and he also in Paris for a conference, and looked all very
well. He has soon finished his astrophysical book, and I believe they
are going to Harvard for a year next September．一− We have got a newvery sympathetic and clever man to the laboratory, Casimir, a Dutch
pupil of Ehrenfest. He is only 20 years but knows already a lot ofphysics. He may be of very great helps for Bohr.

1
0

You got a little greeting from our Conference in the institute?
It was a pleasant time with so many of the old friends, but rather
straining・Scientifically it had, I believe, the importance that severalof us got rid of wrong attempts to cure Dirac s electron theory. As tothis theory the difficulties still remain in spite of so many attempts
to overcome them. For my own part I cannot leave speculating about thistheory though it does not seem to lead to any other result than
Spintrubsinn as Jordan calls it. In order to understand the situation
I have tried to study the assumptions,on which Dirac s theory is based,
a little more closely.

As you know, Dirac takes as a fundamental

assumption for the quantum theoretical one‑body problem that theelectric density should be represented by such a matrix that the
Eigenwerte of the electric charge in an arbitrary volume at a given
time should be 1 and O (the charge of the electron being taken as unit).
Now the charge of the electron can be determined as well byelectrostatic as by magnetic actions; and therefore it seems to me thatthe existence of elementary quantum of electricity requires moreoverthat the amount of electricity flowing through a plane during a certain
time ‑in case of a free electron‑ should be a matrix with the
eigenwerte 1 and O.

This assumption does not follow from the former

assumption and the continuity relation for the electric charge since itwould be too special to assume that the matrices, which represent theelectric current vector and density at a given space time point commute
with one another. Indeed, this would entail that the densities at agiven point at different times would commute,which would contradict thegeneral statistical character of quantum theory. Now I begin to believethat the assumption about the current matrix is not fulfilled in Dirac s
theory and that this is connected with the difficulty with ±E. 工f thisis true ‑‑which I am not yet certain of‑ it might perhaps give somesuggestion as to a modification of Dirac s theory.
You will remember the discussions about the spin of free electrons
going on in the laboratory at the time when you left Copenhagen.

Bohr

has written several sketches to a note about this question,which I hope
he will soon accomplish, since it contains some very interesting

1
1

considerations. 'l'he conclusion is that one can never detect any
influence of Spin in experiments where the path of the electron can befollowed, i.
e., in the region ofgeometrical

optics（ ordinary

mechanics); this does not exclude the possibility of a polarisation of｛＊）free electrons,

but we are not allowed to speak of a Spin magnetic（＊＊）

moment of a free electron.

Also about the question of the B

particles Bohr has written an interesting note,which he has not sent ineither.

He criticizes G. P. Thomson s considerations and points outthat a lack of conservation of energy is quite contrary to the present
form of quantum theory, but that it cannot be beforehand excluded due tothe difficulties of the theory; on the one hand the lack of aninterpretation of the size of the electron in the classical theory, on
the other hand the difficulties of Dirac's theory in high fields (as for
instance in my note in Z. f. Phys.). This was just to give you an ideaof what we have been thinking of this year.

I am very eager to hear

about your own plans. Are you thinking about the Compton effect,where
there seems to be many interesting problems yet?

What do you say toBothe s and Kolhorster s idea that the cosmic radiation is corpuscular?
工 have no great sympathy for the hypothesis of a transformation ofmatter into radiation, so I rather think they are right.

Now the kindest regards from al1 of us, also to your wife and tothe other physicists.
Yours,
Oscar Klein(*)

Mott has written a paper in Proc.Roy. Soc. where he shows that apolarisation would occur in the scattering of electrons by anucleus. Jacobsen has tried to find it, but so far has not
succeeded.

(**) This result is most easily obtained from Dirac s theory, forinstance the problem of reflection at a plane surface can easily begenerally solved, the result being no polarisation.

1
2

Dear Nishina:
工 justwanted to thank you so much for your beautiful gift, it was

too kind of you to think of sending us such a pretty present. We often
miss you!
。R
egards.

Affectionate
Gerda Klein(Post card, Photograph of TEUFELSBRUCKE）
26 July 1929

Treseburg of Harz
Dear Dr.Nishina

I send you the kindnest regards from Harzen, where I am spending mysummer holidays. It is awfully nice here.

Afterwards I shall be in

Berlin for a few o.
ays and then back to the work. I think I shall stayby Prof. Bohr in Tisvilde the first days of August and help himwith hiswork. I hope you are getting on well and look forward to hear a little
from you when you have time

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1
3

The Institute of Physical andTokyo, 25th.Nov. 1929

Chemical Research.
Komagome, Hongo,Tokyo
Dear Professor Bohr,
工t is a long time since I wrote to you last． 工 have had so much to

do for last six months that I have been unable to write to anybody. I
hope you and your family have been all very well.
Mrs. Bohr wrote to me in her last letter that the plan of yourvisit to America and Japan has not yet been fixed in detail. 工 wonder
if you have made it more definite since then.
Professor Nagaoka wants to have a very rough idea about thepossible time you and Mrs. Bohr could come over here． 日e will take careto obtain the sum of ten thousand(l0,000) Yen, which, as I have told
you, we intend to offer you. Since I wrote to you last, there has beena great change in the financial situation of Japan on account of thepolicy taken up by the new Government, the national thrift and thereturn to the gold standard, which will be carried out at the beginningof next year. The former policy is considered to be the way to arriveat the latter. This policy of the Government has shown its effects atevery corner,and it might not be so easy as expected before to find thesource of the above mentioned sum,we do not know as yet. This is thereason why Professor Nagaoka wants to know the very rough time of yourintended visit. As soon as he gets the above matter arranged, I expectthat he will send you a formal letter of invitation. I should therefore
be very much obliged to you, if you would let me know whether you havemade any definite plan about your visit to Japan.
Last September we had a visit of Heisenberg and Dirac on their way
back to Europe.

They gave severa1 lectures each,which were of great

benefit to us. To our regret, however, they stayed only two or three
weeks, which were much too short.

1
4With best wishes to you and all your family for a merry Christmas
and a prosperous New Year,Yours very sincerely
Y. Nishina

Universitetets Institut
for Teoretisk Fysik

Blegdamsvej 15 K￠benhavn ￠20th of December 1929

Dear Dr. Nishina!
I thank you so much for your most kind and interesting letter which
I received the other day. It was awfully kind of you to take time towrite to me, a1though you are so occupied with your work. It was sointeresting to hear about your Japanese house, and how you are gettingon.
We have also had an awfully busy time this autumn. In my summer
holidays 工 had a very nice trip to Germany together with a lady friendof mine, we stayed in Hamburg and Berlin for a few days and spent therest of the time in Harzen. Coming home I went at once up to Tisvilde
and stayed there by Professor Bohrsfor it week. There should be ameeting of Scandinavian scientists here in Copenhagen in the end of
August and Prof. Bohr had to open the meeting with a lecture, so thewhole time in August was taken upwith the preparations for this.

The

opening‑meeting was held in Raadhuset and I was there and heard
Prof. Bohr s lecture; the meetings took a week in al1 and every day
lectures were given of the physicists here at the Institute.
After that time we were stil1 more busy, as Prof. Bohr should
write an article to Universitetets Festskrift. He had postponed it longtime, as he had hoped another professor would have overtaken the task,
but unfortunately he could not,and Prof. B. had to do it himself. There1
5

could not be time enough to write something new, therefore he used threepapers he had written to Naturwissenschaften in the last years; they
were translated into Danish by Dr.Klein, Hr. M￠ller and Prof. Bohr; I
had to short‑,hand write and typewrite it all, so we worked many evenings
and sundays too on it.
Next year there is, as you perhaps know, a possibility of O.
Klein s leaving us in order to go to Stockholm and be professor there,
but it is not decided yet whether he or one of the other three will get
the position. We will miss him very much, especially I think it will be
a great loss for Professor Bohr.

There is at present a young dutch

physicist, Casimir, former assistant of Prof. Ehrenfest in Leiden; hehas been here for some months, is living at the institute in theguest‑rooms. He is a very good help to Prof. Bohr, and we hope he will
stay for some time. Prof.Ehrenfest was here for a few days a fortnight
ago, and Professor Richardson from London has just been here with hiswife and daughter on his way home from Stockholm, he has got the Nobel
prize this year, i.e.the half of it I think,de Broglie got the otherhalf. We were all by Prof. Bohrs last monday night together with theRichardsons.
We have had unusually fine weather the whole autumn, up till now it
is still very mild and now we have already Christmas.

'l'he Christmas

tree is standing in the front of Raadhuset, and the shops are open until
9 in the evening, all people are so busy with their preparations for the
Christmas‑days. 工 myself don t like Christmas much, Christmas songs andtrees and all such things make me feel melancolic. I shall spend
Christmas evening by my uncle and aunt and the other days by somefriends, so perhaps it will be rather pleasant nevertheless.
Sure1y I sha11 write again and te11 you what happens in theInstitute. I quite understand that you have not time to write so often
but I am very glad to hear from you when you have time, your letters are
so interesting, so I read them several times and keep them. Will you
bring my kindest regards to Mr. Kimura, Takamine and Sugiura, when you

1
6

see them.
The kindest regards and the best wishes for a happy new year for
yourself.
Yours very sincerely
Betty Schultz

Blegdamsvej 15 K￠benhavn 0

Universitetets 工nstitut
for Teoretisk Fysik

December 26 1929

Dear Dr. Nishina,
It was a great pleasure to hear from you. 工 have for a very longtime intended to write and before all to thank you for your beautiful
box,which to my wife and me is a nice remembrance of your long stay in
Copenhagen, of which we all think very often.

I have only postponed towrite, because I hoped at the same time to be able to tell.you of myplans and the time of my intended visit to Japan.

Al1 this year,

however, I have been very occupied with duties among which have been the
preparations for a University Aarsskrift of which 工 sendyou a copy at
the same time as a little Danish greeting. Due to this situation I had
to postpone my journey to America and Japan in 1930, but if it suits
your authorities, I shall be delighted to come in the spring of 1931 andto stay a month s time in April and May.

I would propose to give acourse of lectures on the fundamental problems of quantum theory towhich I have given much attention in recent years. My wife as wel1 as
myself look forward very much indeed to seeing your country and our old
friends among your countrymen again.

We are just having Christimas

where the whole family have been talking of you, and we all send you andyour wife our heartiest wishes for a happy new year.
Yours
N. Bohr1
7

Tisvildeleje, August 4th 1930.
Dear Nishina,
工 am very sorry to have delayed so long in answering your kindletter regarding my visit to Japan, but due to various unsuspected
University duties here I have not hitherto been able to make thenecessary disposals for my journey. As you know, I had hoped to come to
Japan next spring, but I have just realised, that due to my work andduties here I shall not be able to leave Copenhagen for a sufficient
length of time during 1931. To my regret I have therefore to postpone
my visit to Japan to the spring of 1932, and I hope that this change inmy plans will not be inconvenient to your university. As for the same
reason I have also had to postpone a visit to America,my wife and I
intend in 1932 to travel round the world through America and to spend amonth s time in Japan.

We look both forward to see our old friends

again and to learn about your country, of which we have recently had
most enthusiastic accounts from Heisenberg and Dirac.

As regards mylectures in Japan I propose to give a course about the principles ofatomic theory. In the last years 工 have given much thought to thissubject,and I hope in a near future to publish my views in book form.
In the institute we miss you very often, but I hope that you havefound good working conditions in Japan. You will be interested to hearthat Jacobsen is just trying some experiments to ascertain, whether the
anomalies in the scattering of various elements for hard radiation foundby English and German physicists are real. So far, his results point to
the non‑existence of these anomalies, but as soon as his conclusions are
more definite, Klein or he will write to you about details.They both
send their kindest regards, and also Miss Schultz, who is at present
here in Tisvilde, asks me to send her greetings and to say, that she
will SOOQ write herself. All the boys,who have not forgotten your play

1
8

with them in the forest, join my wife and me in sending our kindest
regards and best wishes to you and your family.
Yours
N. Bohr

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for Teoretisk Fysik

ei

Universitetets Institut

Dear Nishina,First of all I want to thank you and the other collaborators of theinstitute from your country most heartily for the very beautiful vase
you sent my wife and me at the occasion of the 10 years anniversary of
the institute, and which will always be a treasured remembrance to us.
For an institute 10 years is of course only a short time, but 工 was very
thankful that so many of the old collaborators had remembered theanniversary and for the kind feelings shown me frommany sides by thisoccasion, where 工 had much opportunity to think of all the support
everyone of the collaborators in his own way has given to ourendeavours. We often talk of you,and it would be a great pleasure foreveryone if you once more had opportunity to come to Copenhagen. My
wife and I look also forward very much to our visit to Japan, and I amvery sorry for the repeated delay of our journey which has been caused,however, by various unsuspected duties which have not made it possible
for me to leave Copenhagen 土or the required long time. Even now ourplans are somewhat ur,settled on account of the change in the staff ofthe institute resulting from Klein s appointment in Stockholm.

Ofcourse it has been a great pleasure to me that at length he got thispost in his own country which he has so well deserved, but as you willknow, his departure is a great loss to us, although in M￠1ler, who isdeveloping very promising indeed, we hope to find a good successor to1
9

his post. I look forward, however, to the opportunity to discuss andsettle the plans of my visit to Japan with Nagaoka, from whom I havejust had a few lines from Berlin, and whom we expect here in the courseof a week s time. When I have seen him, I shall write again.
This time I will only once more repeat the heartiest thanks to you
all with the kindest regards and best wishes from my wife and myself.
Yours
Niels Bohr

6. XI. 1932

Dear Professor Bohr,
It is a long time since I received your kind letter as well as aninteresting card from the excursion in Nord Jylland on the occasion ofProfessor Hevesy s visit to Copenhagen. In response I intended to write
to you at that time, but was unable to do so on account of my illness,
which took about six weeks (November 1931 ‑ Jan. 1932), and made me very
busy after recovery owing to the accumulation of everyday business.
Since then I have been lost in silence among my friends in Denmark.
How are you and your family?

I suppose you live now in

Oresboligen paa Carlsberg of which Miss Schultz wrote to me nearly ayear ago. I hope you have more time of your own there. Are there many
people working there?
How is the Institute at Blegdamsvej? Heisenberg wrote to me lastsummer that he was looking forward to visiting Copenhagen in September
when Lord Rutherford would come over to you.

That meeting must, I

suppose, have been very interesting as well as fruitful in view of the20present state of nuclear physics.
In our Institute I have got a room of my own for experimental workand am preparing to do some work on nuclear problems as well as cosmicrays.

I hope to get some results in course of time, but it wi11, I

expect, take some time before we get into any interesting work.

Thedifficulty we meet here in Japan is the lack of fund for such ascientific work. We feel it especially accute at the present ti
me whenour currency has depreciated to less than one half the norm
al value.
I wonder what you are thinking of your journey to America andJapan. We have all been looking forward very much to seeing you andMrs. Bohr here in Japan, and I should like to know whether you arethinking of realising your long planned journey. If so, please let meknow beforehand the time of your projected arrival in this country.
Yours sincerely
Y.Nishina

6.X工. 1932
Dear Miss Schultz,
First of all 工 must apologize you for not having answered to yourkind and interesting letters which I received last year.

When I thinkof Copenhagen, I have always had a very bad conscience that I have notwritten a word to any of my friends. I have a bundle of letters lying
on my table for a year or so and I think I must now begin writing nomatter how busy I am everyday. Since I wrote to you last ‑‑ I do notremember when it was， 工 have had so much to do with the work in our
Institute,where I have now a room of my own for experimental work so I
can do some work. Of course this takes very much tim
e of me and that is2
1

the chief reason why I have been unable to write to you.
At the end of last November, about a year ago, I became ill and forabout six weeks I was in a hospital where I spent Christmas and New
Year. That was not very pleasant. Af‑cer that illness I was not quite
wel1 for a few months, during which different business had accumulated
and took me much time to finish. Now I am quite well and working allright everyday.
At home I am now a father of two boys. The second boy was born
last May and getting on very well although he has taken cold just at thepresent. The first boy is 2
lyears old now and speaks a funny language
which makes us laugh.
How are you since I last heard from you? I hope you are in thebest of your health and happy in your work.

I suppose Professor Bohr

lives in Oresboligen paa Carlsberg， as you wrote to me. How is he andhis family?

I do not know if he has decided to go on to his longplanned world journey. We have been expecting him here for a long timeand I should like to know whether he will come here next year.
日ow is the work going on in the In
stitute?

Are there many people

now? Please remember to all our mutual friends.
With best wishes and remembrances

n

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2
2

The Institute of Physical andTOKYO, 7. April, 1933.

Chemical Research.
Komagome, Hongo, Tokyo
Dear Professor Bohr,I have read in a certain American journal that you are going tovisit Chicago this summer. I do not know whether it is true or not. If
so, I wonder whether you have any intention of extending your journeyover to this country, where we al1 have been, as I so often written toyou, looking forward to your long planned visit. If you come, please
let me know when we could expect you here.
I wrote to you at the beginning of last November and as I have notheard from you，工 presume that you have been very busy as usual. Has
the annual meeting of old Copenhageners taken place this year in theInstitute? I wish I could be present there.
I have lately finished together with my assistant a calculation on
the scattering of neutrons by protons on Heisenberg s theory of nuclei
making a certain assumption of their interaction energy. I hope soon to
publish it in the Scientific Papers of our Institute.
I should be very much obliged to you, if you would send me, in case
it is possible for you to spare, a separate copy of each of thefollowing papers:
1) Your Faraday lecture2) Your lecture at Rome Congress on nuclear problems3) M￠ller s work on the collision problem
I hope that this letter will find you and your family in the bestof health. We are getting on all right in my family. My wife joins me

2
3

in sending kindest regards and best wishes to your family and yourself.

In

ya

−

Y

e
Eh
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c・
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CM

．nL N

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7
. IV. 1933

Dear Miss Schultz,
It is a long time since I last heard from you.

How are you?

I

hope you are quite all right. I saw in a certain American journal that
Professor Bohr is going to visit Chicago this summer. Is that true? If
so, you must certainly be very busy for different preparations.
Is a meeting of old Copenhageners taking place this year in theInstitute, as has been usually the case at this time every year? Throughdifferent publications I understand that a good many able physicists
have lately stayed in the Institute. Has there been much change in theInstitute?
To‑day I have also written to Professor Bohr and asked him to sendme, if possible, a separate copy of the following papers.
1) Professor Bohr S Faraday lecture2) Professor Bohr s lecture at Rome Congress.
3) Dr.M￠ller s papers
Annalen der Physik, Bd. 14, S. 531, 1932
Zs. f. Phys. Bd. 70, s. 786, 1931
I do not know whether you have any of them still left, if there is
any which you could spare,please send them to me.
I am quite all right but am very busy with different matters2
4concerning our laboratory work, on account of which 工 have very little
time to write letters to my friends.

Does Dr. Klein come often to

Copenhagen? I have received his very kind letter a long time ago,but 工
have not yet answered to him, and 工 have a very bad conscience.

I amthinking of writing to him soon.
In my family all are going on all right. The boys are growing up
gradually. 工t is very interesting to observe how they grow and how they
begin to do different things.
I suppose that this letter will come to you when the Danish forest
is in a fresh green.

I cannot forget that beautiful colour, whichbrings me back all nice remembrances of what I have had in Denmark.
Please remember me to al1 in the Institute, who I hope are working
very well.
I hope that this letter will find you in the best of your health.

V4a

I n

cl

e
rh
−
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QM

nN

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−
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With best wishes and kindest remembrances,K￠benhavn 26/4 1933
Dear Dr. Nishina!
I thank you so much for your very kind letter, which I have justreceived, and also for the former letter, which I feel much ashamed
having not answered long ago. But I think you will understand how busy
I have been the whole winter and spring, when I tell you that Prof. Bohr2
5

has now really left for his journey to America．

日e left on ・the 19.

April together with Mrs. Bohr, and they go over England to America,
where Prof. B shall lecture in Balltimore, Philadelphia, Ohio, Pasadena,
Ann Arbor and also at the Chicago exhibition. On account of the journey
there was no times for the usual Easter conference this year, but it
will take place in September instead.

It is a very bad thing, thatJapan is so far away, it would have been so nice if you could come too
for the conference, it is always so pleasant to see our old friend
again. This year we have had Dr. Kopfermann from Berlin, Dr.Weisskopf,
Dr.Placzek, Prof. Rosenfeld and a young Indian Chandrasekhar, here.
Also Bloch and Delbruck have been here for small visits. Ebbe Rasmussen
is this year staying in Berlin on a Rockefeller stipend. Prof.Klein
was here in December to help Prof.Bohr with a paper on Light and Lifeof which I send you a copy, which may perhaps interest you. Here has
not been much change in the institute, Dr.Jacobsen, who asks me to beremembered to you, Ebbe Rasmussen and I are still assistants, and Chr.
M￠ller is Lektor in Klein s place.

Also S.Werner is still working

here.Dr.Jacobsen and his family are now living in Professor Bohr s oldhouse, afte工 they have gone to Carlsberg・On the older side of theinstitute, opposite Prof. Bohr s house they are at present building amathematical institute in connection with our institute, themathematicians shall use our lecture‑room and we shall get a few
laboratory rooms in the basement of the new institute instead. Prof.
Harald Bohr is the leader.
I am glad to hear that you and your family are in good health.

I

would like very much to see the boys, I am sure they are lovely. I
thought very much of you by reading in the newspaper about the awful
war, but you have not been in war? have you? And how about Kimura andSugiura and Aoyama？ 工 hope none of them have been in the war.
I don t know whether Prof. Bohr has written to you from hisjourney.

He has spoken very often of writing, but you know how it goessometimes, he intends, I think, to propose to go to Japan in 1935, thenChristian will be student and go with him as secretary; I think that is2
6

the intention, if it suits you. All the Bohr‑boys have grown up very
much, Christian is quite a young man now. Aage and Ernst are big boys
too, but still very sweet. The Kleins have in the autumn got a little
girl, they have now 5 children.
工 have myself been a little tired and nervous in the winter, but

now I hope it will be better, when Prof. Bohr is away, there is not somuch to do, and I can go every day early in the afternoon. The forest
is not yet green, but it will come in a few weeks.

Dr. Kopfermann andhis wife who shall be here the whole year, are now living in Hellerup by
Erik Thalbitzer, where Kimura stayed,when he was here.
I send you by the same post as printed matter the reprints you
wished, and send the kindest regards and best wishes for you and yourfamily.
Yours very sincerely
Betty Schultz
P.
S. I shall not be so slow in letter writing in the future.

18.V工
工 ． 1933
Dear Miss Schultz,
I thank you very much for your very kind and interesting letter ofthe 26th April. 工 have not heard from Copenhagen (the fault is mine) solong that everything was obscure to me, and your letter brought to me
all what I wanted to know. I felt as if things were shown under the day
light.

I intended to answer to you soon, but 7 weeks have since thengone away.
I am very glad to hear that you are very well now.

How is the27

weather this summer in Copenhagen? Have you gone away for holidays?
How are they getting on in the Institute?
I have not heard from Professor Bohr in America. A few days ago,
Gamow in Leningrad sent us a telegram and asked us if we could invite
Professor Bohr here in August then they would do so in September on his
way back to Copenhagen. But August is a bad season here, it is too hot
and is not nice for Professor and Mrs. Bohr to travel round at theearliest September. We sent a wire to Russia informing themof thesecircumstances, we have not heard from them any more, so I think theyalso have given it up. I knew from your letter that Professor Bohr will
be back in Copenhagen for September conference, therefore it is notpossible for him to come to Japan and stay unti1 October. If he could,
we would have invited them here. Moreover, I know from your letter that
Professor intends to come to us in 1935, so we thought it better to wait
until he has more time to stay here. Professor Bohr told to Professor
Nagaoka a few years ago that he will visit us in 1933, so we had
expected him here this year until 工 received your letter fromwhich welearned that he is not coming this year. Professor Bohr has not written
to me for a long time and it was difficult for me to know whether hecomes to Japan or not. If he comes, we have to do some preparations fordifferent matters.

I hope Professor and Mrs. Bohr will carry out theirlong planned journey to Japan in 1935,and if so, I should like to know
it beforehand.

If he cannot write to me, please you let me know. Evenif he does not come, we should like to be informed of it as early as
possible.
You wrote to me in your last letter about the war. It is not so
bad at a11 as you think it in Europe.

We do not take it so serious.

You asked if we have been to war. No, none of us has the least chanceof going to war. We are all doing physics as peacefully as ever.

Only

difference is that Japanese currency has gone down nearly to half its
normal value and it is very difficult to buy things from abroad.

Apartfrom such economical questions, we are all getting on very peacefully
and very well.

2
8

Have Dr. Klein and his family come to Copenhagen this summer?

I

have really a very bad conscience that I have not answered his kindletter. When you see them, please apologize it for me and tell him that
I amwriting as soon as I get time to do it.
Al1 the reprints you have sent to me last time are very useful forme and I should be much obliged, if you would send me in future theseparate copies of papers published from the Institute.
It is very hot now in Tokyo and is very disagreeable, but in myfamiliy everybody is getting on all right. About a month ago 工 went to
the north part of Japan (Hokkaido) to give regular lectures to
University students there, lectured 2 or 3 hours a day and did it for a
fortnight. It was rather tiring・ I have to do it again in September.
I send you my best wishes and kindest remembrances.
Yours sincerely
Y. Nishina
P.
S. Please remember me to Professor and Mrs. Bohr when they comeback and also to all in the Inst土tute.

The Institute of Physical andTOKYO, 19.July, 1933.

Chemical Research.
Komagome, Hongo, Tokyo
Dear Professor Bohr,As I think that this letter cannot catch you in America, I send it
to Copenhagen. Some days ago, Gamow sent us a telegram asking whether
we could invite you here in August on your way back to Copenhagen. 工f29

we could, they would invite you to Russia in September on your way homefrom here. The month August, however, is very hot and is not agreeable
both for lecturing and sightseeing. One must wait at the earliest till
the middle of September. To this effect we answered to Russia and we do
not hear any more from them. We know that it is probably not possible
for you to stay here from the middle of September to the middle of
October say, because Miss Schultz wrote to me at the end of April thatyou intend to have a meeting of old Copenhageners at Blegdamsvej in
September. Otherwise we would have invited you here in Japan. I heardthat you intend to come here in 1935, is that your plan? You know that
we all have been waiting to see you here in this country and I really
hope that you will carry out your plan as early as possible.
I suppose that you have had much to discuss and to see in America
and that you are now glad to come home to have a peaceful rest.
Sending best wishes and kindest regards to Mrs. Bohr and yourself
also frommy wife,

vea

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for Teoretisk Fysik

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・−

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Universitetets 工nstitut

Blegdamsvej 15, K￠benhavn ￠6 Novbr. 1933.

Dear Dr. Nishina!
I thank you so much for your kind letter from July 19. I am quite
astonished that so long time has passed since I got it, but time flies
so quickly. It was all right what you wrote about not inviting Prof.
Bohr to Japan and Russia this summer, he could not have come, he has notlater spoken about going to Japan in 1935, but I think it is his

30intention. He will write to you himself; every time we are writing alist of letters to be written, your name is there. Prof. Bohr says We
shall write to Nishina, put him first on the list, ~: e write to‑day or
to‑morrow，一一 but you know, how it goes. This fortnight Prof. B has

been in Brussels for the Solvay conference and before that he was very
busy with the proof of a work of him and Rosenfeld which I think willsoon appear. And in September the conference took much time, here wereplenty of people this year, 44‑45 foreign guests, all the old ones,
Kramers, Heisenberg, Fowler, Dirac, Heitler, Klein, Casimir and manyothers. Have you heard the sad news of Professor Ehrenfest s death? He
was here during the conference and lived by Prof. Bohrs at Carlsberg,
but seemed rather depressed, and 4 days after he left we heard, that hehad shot himself and his son.

工t was terrible, we were all quite

shocked to hear it. Also Mrs.Maar has died; she was suddenly taken ill
and died after 4‑5 days. Do you remember Mr B. B. Ray? Yes,you do,he
was here at the same time as you, he was here on a small visit a few
days ago, he is going to work with Prof. Siegbahn in Upsala for the
winter, and stayed here for a fortnight to see Prof. Bohr, but
unfortunately, it was just the fortnight where Prof. B was in Brussels,
so he did not see him. Ray looked quite like himself 7 years ago, it
was funny to see him. Klein has been here for short visits, during theconference and once before, but Mrs. Klein I have not seen for very longtime. You know they have got a daughter too, 5 children in all havethey.

Kramers has got a son this summer and was very proud of him, andKuhn had, when he was here in September a daughter of 3 weeks．
一− We
have had an unusually fine summer this year, even from May and up till
September it has been summer, we have not had such a summer since 1914.
I did not go far away this summer in the holidays; it is so difficult totravel in Germany at present, and our Danish crowr, is of so little valuethat most people stayed at home this year. I spent my holidays at theseaside, by some friends in Lisleje and enjoyed the water and the heatvery much ‑Have I told you that a mathematical institute has been

bui1t in connection with our institute. Prof. Harald Bohr is director
of it.

Prof.Bohr thinks that it shall be good for everythin
g but itlooks bad, quite spoils the good appearance of our institute. I enclose3
1

a small picture of the old institute, if you cannot remember any longer
how it looked.
Gamow was here a few days on his way to Brussels with his wife, she
was very young and sweet, but she spoke only Russian, so noboday could
speak with her.
Now 工 will only send you the kindest regards and hope that you andyour family are still getting on very well.
v
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for Teoretisk Fysik

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Universitetets 工nstitut

Blegdamsvej 15, K￠benhavn !
2).
January 26th 1934.

Dear Nishina,
I know that you won t think we have forgotten you, although I to mygreat regret have not written to you for so long.

Indeed, in thelaboratory we miss your experience and helpfulness constantly, andbesides we are in our theoretical discussions almost daily remin・
ded ofthe beautiful work you made just before you left in collaboration with
Klein, whom you know that we also miss very much after he left us for
Stockholm, from where we still often enjoy a short visit of him.

Thefamous formula which was the result of this work is not only, as I neednot say, the basis for the interpretation of the scattering measurements
in which we ‑ not least due to Jacobsen s work‑

are intenselyinterested, but the striking confirmation which this formula has
obtained became soon the main support for the essential correctness of
Dirac's theory when it was apparently confronted with so many gravedifficulties. You can imagine the enthusiasm with which we here as

32everywhere have followed the marvellous recent development of Dirac s
views and the discovery of the positive electron. ,Just in these days
Jacobsen has got some beautiful Wilson photographs of positive ray
tracks produced by y‑rays in Argon, and Williams, who is at present
working here as Rockefeller fellow, has just sent a note to Nature aboutsome scattering experiments which gives an independent support for theview that the so‑called nuclear scattering of y‑rays is essentially due
to the annihilation of positive electrons produced by the rays in the
scattering material. Of theoreticians are at present besides M￠1ler,
who is now Klein s successor as Lektor, Rosenfeld, Teller, Placzek,
Plesset and Weizsacker working here.

We are at the moment especiallyinterested in the problem of the limitation of the correspondence
methods of quantum theory. By the same post 工 amsending you a copy ofa recent paper of Rosenfeld and myself on the measurability ofelectromagnetic fields in which we have shown that the current criticism
of the quantum electromagnetic theory is not sufficiently well founded.
As stressed in our paper, we get, however, thereby not closer to thesolution of the fundamental problem of the proper harmonising of the
field theory and the atomic theory, and at present I am occupied withthe closer study of the peculiar limitation of the correspondence
argument with which this problem presents us.
Although I think that you may be interested to hear a little about
what is going on here, I shal1 not on this occasion tire you further
with such details and shall pass to the other point, of which I havestill worse conscience not to have written to you, namely the kind
invitation to come to Japan. My wife as well as I have all these years
been looking forward very much to this journey ar.
d have been very sorry
to have had to postpone it for so long due to my many obligations here
and unforeseen arrangements as our journey to America last spring,where
I had to go as official representative to the scientific meeting inconnection with the world exhibition in Chicago. Also at the moment I
have much to take care of in connection with the extention andreconstruction of the institute, but after this there is no hindrance
for our journey and if it suits the Japanese institutions we should take3
3

great pleasure in coming to Japan in the spring of 1935. This summer
Christian will also have passed his student examinations what will makeit easier for us to travel so far, and we have even thought to take him,
who intends to study physics, with us as my secretary at the elaborationof my lectures in Japan. As regards these I propose to give a survey ofthe evolution and present state of the principles of atomic theory, andI think that I could give a fairly rounded exposition in about 8
lectures or perhaps a few more extending over about a month's time.

I

should be very glad to know, if this is suitable and should also be muchobliged if you would write to me, how it stands now with all practicalaspects of the invitation and about what advice you may be able to give
us about our journey and about the best time for our visit to Japan.
With kindest regards to yourself and your wife and all common
friends in Japan from all in the institute and from the whole family,
Yours,
Niels BohrThe Institute of Physical andTOKYO, 21.March, 1934.

Chemical Research
Komagome, Hongo,Tokyo
Dear Professor Bohr,I thank you very much indeed for your kind and interesting letterof the 26th. January, which, to my regret, I have not been able toanswer owing to different reasons for about three weeks.
First of all we are all very pleased to hear that you are going torealize the long planned journey to Japan in the spring of 1935. We
shall be much delighted to welcome Mrs. Bohr and yourself together with

34

Christian in our country.
As regards your lectures to be given here, we agree to yourproposal with much pleasure. As you know, we are situated very far fromthe centres of the research activities in the modern physics and we wish
very much to avai1 ourse1ves of this opportunity and come into contact
with the latest developments as well as the new tendencies in thequantum theory. We should like therefore to have also some occasions
for free talks and discussions on various problems.
With respect to the best time of your stay in Japan, I shouldsuggest you to be here between the beginning of April and the end ofMay, in case you come in the spring as you wrote to me. The
corresponding time in the autumn would be between the beginning of
October and the end of November. Cherry trees blossom usually from the
beginning till the middle or down to about the end of April; it depends
on the weather of the year and the place in Japan. Other flowers andblossoms come usually in April and May or in June and trees become green
usually at the end of April. The rain season begins at about the middleof June and lasts for nearly a month, after which the hot season sets in
immediately.
I do not know which route you would like to choose in coming toJapan.

There are three ways. The shortest one would be through Russia

and Siberia. It is a long train journey and takes a little more than afortnight. The railway fare (1st. class) is roughly 5ιO pounds sterling
per person excluding charges for meals and probably for sleeper too.
The second one is via Canada or the u.S.A. and you know the way except
the Pacific Ocean, which takes between 10 and 16 days according as thesteamer and the route you choose (Vancouver −ー
今 Yokohama, Seattle ~Yokohama or San Francisco −ー−，， Hawaii −ー−，， Yokohama). This journey takes
about 25 days.

The through fare (1st. class all the way) 90 pounds

sterling excluding charges for express train, sleeper and meals in
Canada or the U.S.A. The third one is to take a steamer either fromEngland, from Marseilles or from Naples directly to Yokohama via Suez,

3
5

Ceylon, Singapore, Hongkong and Shanghai.

It is a long journey andtakes about 37 or 43 days from London and 33 or 38 days from Marseilles.
工t depends on the steamer.

The fare is about 100 pounds sterling perperson. Your choice largely depends on your taste and also on whatarrangements you might make en route.

I am sending you by a separate

post some sailing schedules, tariff lists and plans of some steamers
belonging to the Nippon Yusen Kaisha (N.
Y.
K.), a Japanese steamshipcompany for these journeys. If one makes use of the special round‑the‑world tour arranged by the N.
Y.
K. (probably by other steamship company
tool the fare (1st. classl per person for the whole round journey(London −ー争 工ndian Ocean −一今 Japan −一予 Pacific Ocean −一・＞ Canada or theU.
S.
A. 一一争 Atlantic Ocean 一一争 London) is about 166 pounds sterling
excluding charges for express train, sleeper and meals in Canada or the
U.
S.
A.The ticket is valid for 24 months from the date of departure.
As regards the amount of money we offer you, it was ten thousand
yen when we invited you at first,as you might remember;this made about
a thousand pounds sterling at that time.

Since then, however, muchchange has taken place in the financial situation of the world.
Japanese currency has depriciated very much and at present ten thousand
yen makes only five hundred pounds sterling roughly.The cost of living
and of general things inside Japan has nevertheless remained the same orgone up a little if any. This means that it is very difficult for us atpresent to make any・
contracts with or buy things fromwestern countries.
The ten thousand yen in Japanese currency which we offered you long ago,
is of course still valid but we do not know as yet whether it ispossible for us to increase the sum in view of the depreciation of yen.
I have talked it with Professor Nagaoka who supervises the whole matter,but we did not come to any positive conclusion. Ten thousand yen is
decidedly insufficient for the expense of the whole journey for three
persons, as you see from the above description of the fares and we aretrying to increase it, but we do not know yet how far it is possible to
do so under the present financial conditions.

This is the essential

point and as long as it is not settled, our invitation is incomplete.
As soon as the problem is settled, I shall write to you;but it does not36seem to be done quite soon and 工 have made up my mind to write thisletter already before its final solution, in order to give you
beforehand the idea about the situation, which may of course change
better or. worse before next year; we can not foresee it. In any case itis our next step to inform you of this point.
I hope I have written as much as possible about what you want toknow. If you want anything more, please do not hesitate to write to me,
I am very pleased to give you any information.

In case you decideanything either in the positive or in the negative, please let me know
as soon as possible, because I have to do arrangements and to be readyfor what you want to do or not to do. As regards the arrangements foryour journey, I shall do anything for you if you like, please letmeknow.
I was much interested to hear from you what isscientifically in your Institute.

going

on

Your joint work with Rosenfeld

arrived here some days ago, I have not read it yet but am very muchinterested to do so. We shall soon have discussions on the paper in ourlaboratory.

The development and the difficulties of the quantum

electrodynamics have absorbed our attention ever since Dirac and
Heisenberg came here. We have had recently discussions on the works ofBorn and Wentzel but have not come to any conclusion. Their efforts forthe modification of the classical electrodynamics itself can be welljustified but we could not find out whether it was done in the right
direction.
Since I came back here in Japan, I have been chiefly interested in
the atomic nucleus and the cosmic rays. I and my assistants calculated
some time ago the absorption of neutrons through matter; we have notpublished the results but hope to do so soon. We made also some
calculations on the collision (elastic as well as radiative) between the
proton and the neutron. The results depend however, much on the exact
mass of the neutron, which seems to be unsettled at present and we havetherefore postponed the publication for nearly a year.

37Ever since the discovery of the positive electron by Anderson, we
have been much interested in its theoretical interpretation. We
published here in Tokyo a short note on this problem in July last and we
found later that different people explained it in the same way ‑ on
Dirac theory. For nearly a year we have been doing calculations on theprobability of the photo‑electric production of positive electrons.

工t

has taken a long time but we have at last obtained the final results,
among which we have some to be compared with those of Oppenheimer andPlesset as wel1 as of Reitler and Sauter. Our results are quite
different from the former but agree with the latter.
In the experimental side,we began about two years ago to make thestudy of cosmic ray particles by means of the Wilson cloud‑chamber
placed in a magnetic field. We designed the apparatus in such a way
that

two Geiger‑Muller

tube‑countersin coincidence actuate theexpansion of the chamber and get automatically the photograph of theparticle which started the conincidence of the counters. We found laterthat Blackett and Occhialini had started the same work based on exactly
the same principle and obtained the well known results. It has taken along time for us to have the apparatus in working conditions but inNovember last we succeeded at last in getting good photographs ofcosmic‑ray tracks, we are trying now to get more interesting results.
Quite recently we have also examined with a Wilson chamber theartificial radioactivity of Curie‑Joliot and Joliot.

We found thesimilar energy distribution and energy limit as was reported by the
French discoverers. It is altogether a very interesting phenomena.
We have been also making preparations for the study on theartificial disintegrations of light nuclei with protons and diplons.The
progress has been slow but hope to start the experiments very soon. We
are also doing experiments on the loss of energy of neutrons as wel1 as
positive electrons in passing through matter. The above is the all what
is going on in my laboratory. As you see, they are all in a preparatory
stage; we hope to get some interesting results which we can show you

3
8

when you come here.
With kindest regards to Mrs. Bohr, yourself and your whole family
from my family and myself, and with best wishes to all in yourinstitute,Yours
Y.Nishina

Blegdamsvej 15, K￠benhavn ￠.

Universitetets Institut

5th of July 1934.

for Teoretisk Fysik
Dear Dr. Nishina,

I must just write you a fewwords to tell you about the very sad
accident which has just happened.

Professor Bohr's eldest son,

Christian, has died last Monday, drowned on a sailing trip to Norway.
Every summer Prof. 号ohr sails for a fortnight with Prof. Bjerrum and Dr・・Chiewitz and Mr. Hendriksen in Prof. Bjerrum s boat, and they・started
last sunday for a trip to Norway; Christian should be with them only to
Norway where he should join some of his friends for a walking trip． 工t
was blowing rather hard both sunday and monday, and monday evening when
they were outside Varberg in Sweden Christian was thrown 0ver board by
the waves and drowned.

They stayed for some time with the boat andtried to find him, but did not succeed, so he has not yet been found.
Prof. Bohr and Prof. Bjerrum went home in the night to '
I
'
i
s
v
i
l
d
e
, whereMrs. Bohr and the other children had just come.

They are of course

awfully depressed. Christian has just been a student, had got a veryfine examination last week. We are all very sorry, can hardly think ofanything else.
We have Prof. Franck here now for some years,and also Prof. Hevesy

39

will come in the autumn with his family and stay here.

Otherwise

everything is going on as usual.
While I am writing 工 should just ask you,do you think there is any
possibility for a young Danish girl to get a position as nurse in Japan?
It is a young lady of my acquaintances,.
who has a position in an office,but she is tired of it and has always wished to go out and see somethingelse, she has been in England for some time, but now it is not possible
for foreigners to get positions there,and she also wishes to go much
farther away, and she thinks Japan must be the most wonderful place tolive in． 工t is not very likely,that Japaneses would have a Danish

nurse, I suppose? But when you once write to me, you will perhaps tell,
if it is quite out of question; I suppose it is, but 工 promisedher to（＊）

ask you.
工 hope that you and your family are in good health. We have
had very fine summer weather here since beginning of May, so I hope itwill continue so also in my summer holidays.

工 had thought I shouldhave quite a long holiday this year, because Prof. Bohr after his
sailing trip intended to go to Island for some weeks together with Hans
and Christian, but now he has given up everything of course.

They will

stay in Tisvilde, and Prof. Harald Bohr told me just that he would takethe two smallest boys with him to Alps. Prof. and Mrs. Bohr have beenin Russia this spring and have had a most interesting time there. At
present Landau is here and besides him Placzek, Plesset, Williams,
Teller, Proca, Solomon and two young German people of Prof.Franck s
pupils. If you see Kimura and Sugiura and other of ou工 friends you willtell them about Christian.
The kindest regards and best wishes for youself and your family,
Yours sincerely,
Betty Schultz(*)

Also if there should be English families, she is speaking English.

40

TOKYO, 2.Aug. 1934.

The Institute of Physical andChemical Research.
Komagome, Hongo,Tokyo
Dear Professor and Mrs. Bohr,I have just been informed by Miss Schultz of the tragic loss ofChristian and we are greatly shocked and deeply grieved. It must havebeen a terrible blow and an unbearable affliction for you to suffer suchan irreparable loss. There is no consolation for so great a misfortune
and 工 tell you how much my wife and I as well as all your Japanese
friends here feel for you in your great sorrow,which, we know, nothing
but time can soften.
Although it is painful for me to open your grief afresh, I cannot
help informing you that we have been so much looking forward to having
Christian together with both of you in Japan next year. We hope verymuch indeed that you wi11 not abandon your intention of visiting ourcountry.

Probably this journey will divert your mind and bring comfort

to you.
My wife as well as all Japanese friends of your Institute join me
in sending you our deepest sympathies.
With kindet regards
Yours sincerely
Y. Nishina
p.s. Professor Nagaoka who has recently recovered fromhis threemonths' illness is now trying to settle thefinancialquestionconcerning our invitation of you to this country. As soon as it is madedefinite, I shall write to you about the matter.

41

The 工nstitute of Physical andTOKYO, 2.Aug. 1934.

Chemical Research.
Komagome, Hongo, Tokyo
Dear Miss Schultz,
I thank you very much indeed for your kind letter of the 5th.
July,which gave al1 of us a great shock and a deep sorrow. I can very
wel1 imagine how much Prof. Bohr, Mrs. Bohr and whole the family wereplunged into a great affliction and sorrow by the death of Christian,
who was one of the nicest boy to my memory. As you know we expected him
here with Prof. Bohr and Mrs. Bohr next year. 工 hope they have not too
much suffered from this sad accident.
With regard to your inquiry about a position as a nurse for yourfriend, I am very sorry to say that it is, as far as 工 know,nearly
impossible to find such a position among Japanese family.

I have notheard any person having an European or American nurse. The reason is, I
suppose, that the salary for foreigners are very much higher than forJapanese and I think it is almost prohibitively expensive to have such anurse at least for an average Japanese family. Whether there is any
possibility of getting any position for a Danish girl in this country, I
shal1 make inquiry of the Danish Consul here,who must know better thananyone else about such a matter. 工 shall visit him as soon as I gettime and let you know the results, but I expect that the answer will be
negative.
I must apologize you for not having written to you for such a longtime during which I received your kind letter two or three tim
es. I
have recently become more and more occupied with the daily business andI have hardly any time for writing a letter to any of my friends except
for a necessary business. Such a state of life is not very interesting.
Your kind letter always reminds me of the nice time I spent in
Copenhagen and at the same time it keeps me in touch with the present
situation at Blegdamsvej. I thank you for this very much indeed and42

shall be obliged to you immensely for your doing so in future.
I and my family are getting on quite all right.. Our boys, one four
years old and the other two, are glowing up rapidly. This summer wehave had an unusual weather. For three weeks or more we have seldom
seen the sun, it rains very often and is gloo
my. One advantage is thatthe temperature is not so unpleasantly high as usually the case at thistime of the year and we can work without much strain.
You wrote to me that Prof. Hevesy will come to Copenhagen with hisfamily. Do they stay for a short time? Please remember me to them.
With kindest rem
embrances and best wishes frommy family andmyself

v
a
en

la

r
eh
c
s
−
・

n ・l
iN
・
y
S

s

r
u
o
y

Please remember me to al1 our mutual friends in the Institute.

Ishould be much obliged to you, if you would tell any book‑shop to sendme 主
主2 copies of Prof. Bohr and Rosenfeld s paper published recently in
Copenhagen, a copy of which you have kindly sent to me. 工 shall pay the
expense to the book‑shop as soon as 工 get the copies.

d

n
a

ly

o

cT

SE

a
K
cho

−．
v
aa ︐
heo

i
唱

P5 9
en
fRO
OH

TAYA

no

ea ︐
tCe
u
m
tm
o
− −−
eqd
tha
scm

h
T

e

TOKYO, 7. Sept., 1934.

Dear Professor Bohr,
Professor Nagaoka who has been arranging the monetary question
concerning our invitation of you to Japan has requested me to inform youthat you may take the matter as being nearly settled now.

We should

43

like to offer you the sum of twenty thousand yen (a litte more than athousand pounds sterling at the present exchange rate) including yourtotal travelling expenses.

As soon as the matter is finally fixed, weshall send you a telegram. We should like very much to know whether you
could come over here in the spring or autumn in 1935.
With best wishes and kindest remembrances to your family andyourself
Yours sincerely,
Y. Nishina
P.
S. To‑morrow I shal1 leave Tokyo for Sapporo, where 工 shall givelectures to the university students for about a fortnight. 工t is in thenorth‑east and takes nearly thirty hours to get there.

When I comeback, I hope to write to you again.

Universitetets Institut
for Teoretisk Fysik

Blegdamsvej 15, K￠benhavn 0.
13. September 1934.

Dear Nishina,
My wife and I thank you and Mrs. Nishina for your warm sympathy in
our sorrow. We often think of the happy times when you were here and ofyour great kindness to all the boys. Christian as well as we had been
looking forward with so great expectations to our planned visit to Japannext spring. We are thankful for your kind thought that such a journey
might be a comfort to us in these sad days, but 工 am sorry to say that
under the present circumstances it will be quite impossible for us thisyear to leave our home and the other boys, for whom Christian s death,as you will understand, has also been a terrible blow. I might suggestthat we come to Japan in the spring of 1937,at what time we would take4
4Hans,who is now quite a big boy and who will then have finished school,with us.

工 need not say, how sorry I am that after a11 the kindness

extended to us by you and our other Japanese friends by your so often
and so kindly repeated invitation we shall disappoint you again,but I
am convinced that you will understand our situation, and I ask you
kindly to extend my sincere regret and thanks to Professor Nagaoka.
With our kindest regards and best wishes,
yours ever,Niels Bohr

Copenhagen, September 14. 1934.
Dear Dr. Nishina,
Professor Bohr has asked me to send you the enclosed speech, which
he gave by Christian s funeral. We are all very glad that they havefound him，工 think it is 3 weeks ago, and Professor Bohr went up to takehim home together with Dr. Chiewitz. He was found almost on the sameplace where he had gone down. They took him home to Carlsberg and there
was a quite quiet funeral, where Professor Bohr spoke and a pianist
played, and then he was taken to the "Krematorium and burned.
I thank you very much for your kind letter and for your kind
informations about the possibilities for the young Danish girl for goingto Japan. Of course we thought there was no great possibility for it,
and I ask you kindly to take nomore trouble in this matter, please.
You asked for Prof. Hevesy? Yes, he will come with his family andhave hired a flat and they are going to live here for some years. Prof.
Franck is already here, as I think I have told you. Just in these days

4
5

also Weiszacker, Teller, Placzek, Wheeler, Steensholt and Delbruck are
here. Klein has been here but has left again.

There shall as every

year be some discussions here these weeks, but this year it will ofcourse be quiet, no festivities at Carlsberg.
Professor Bohr was very glad for your very kind letter, he also got
so kind letters from Kimura and Takamine; he often speaks of you andintends to write to you sometimes, but you know howmuch here is to doalways, therefore it does not happen so often. It is a great pleasure
to hear, that you and your family are in good health, I wish 工 could see
the boys, I am sure they are lovely.
Kindest regards and best wishes for you and your family,

z

hu

︐
︑
ム
↑
Vし
4U

ec

cva

rnb
ム
︑
e

O

V品

nt
t
se
−
・ B
s
r
u

The Institute of Physical andTOKYO, 28. Sept. 1934.

Chemical Research.
Komagome, Hongo,Tokyo
Dear Professor and Mrs. Bohr,In order to express our affections towards our beloved Christian,
we seven Japanese physicists who have stayed in your Institute, send you
by a separate parcel post a pair of vases to his memory.

We should bevery much obliged to you, if you would place them in front of his grave
or at any suitable place in its neighbourhood. The inscription is
written in Japanese and the translation may read as follows, although it
does not express the original meaning exactly. On one of themTo the Memory of Christian Bohr,46

July, 1934.
On the other, the names in Japanese alphabetical order of the sevencontributors:
Shin ichi Aoyama, Kenjiro Kimura, Yoshikatsu Sugiura,
Toshio Takamine, Yoshio Nishina, Mitsuharu Fukuda,
Takeo Hori.
We hope that some one of us may come to Copenhagen some day, bringsome flowers in these vases and renew the cherished memory of those pastdays on which we played together with dear Christian and other niceboys.
With best wishes and kindest remembrances from us all
Yours sincerely
Y. Nishina
P.S. The parcel will come to you via Indian Ocean and will take atleast two months from this date.

The Institute of Physical andTOKYO, 28. Sept. 1934.

Chemical Research.
Komagome, Hongo, Tokyo
Dear Miss Schultz,
I thank you very much for your kindness in sending me four copies
of Professor Bohr and Dr. Rosenfelds paper. We can save much time now.
If it is necessary to pay for them, please let me know.

47

工 should like to ask you to do another favour for me. To‑day weseven Japanese physicists who have stayed in Copenhagen, have sent toProfessor Bohr by a separate post a pair of vases to the memory of our
beloved Christian.

We do not know whether it is necessary to pay thecustom duty for such sort of things in Denmark. At all events we should
not like that Professor Bohr has to pay the duty and we have tried tosend it free from duty or if possible, to pay it beforehand here inTokyo, but we have not succeeded in either ways and have had to send
them as an ordinary parcel post. In case it is necessary to pay thecustom duty at Copenhagen, I should be very much obliged to you, if you
would be so kind and arrange so that your 工nstitute or some person would
pay the duty for us and you would let me know the amount payed, then I
should send the sum back to you at once. We thought at first to sendsome money to you for this purpose but we have no idea about the amount.
We have therefore no other way than to ask you to do the above favour
for us and I hope that it would not trouble you too much.
The other day I went to see the honorary consul of Denmark here inTokyo and asked about the position for your friend of whomyou wrote tome last time. His wife told me that if your friend is a professional
nurse in a hospital, there may be a possibility of finding a position,
but since it does not seem from your letter that it is the case withyour friend, it is very difficult to get a position here in Japan. She
promised me, however, to ask her friends if there is any position foryour friend and to let me know the results. At the same time she addedthat the Scandinavian girls who have sought a position here just as in
the case of your friend, have generally not been very satisfied after
having been employed,because the relations between the employer and theemployee are different from those in Scandinavian countries.

If they

have a special profession, it is of course quite a different matter. In
any case I shall let you know as soon as I receive the answer from theDanish consul, but I am rather pessimistic about the result.
About a week ago we have experienced a terrible storm in the middle
part of Japan. It caused a great disaster destroying nearly every thing

48

in its passage and killing thousands of people. The wind was so strongthat an express train was blown down on the railway while passing on thebridge.

It was fortunate that the train did not fall into the river,still a number of people was killed. This time Tokyo has escaped fromsuch a great damage. Osaka was the centre of the disaster and we expectthat it will take a long time to recover from the suffering・How did you spend this summer?

I hope you are getting on very

well. Please remember me to all in the Institute.
With best wishes
Yours sincerely
Y.Nishina
P.S. The parcel post comes to you via Indian Ocean, it will take atleast two months from this date.

Universitetets Institut
for Teoretisk Fysik

Blegdamsvej 15, K￠ben)1avn ￠.
November 30. 1934.

Dear Nishina,
I cannot express, how deeply moved my wife and 工 are for the great
faithfulness you and our other Japanese friends have shown the memory of
our beloved Christian by sending us the beautiful memorial vases which
we treasure most highly. They・arrived just before his birthday on the
25. of November, where we had a little solemnity in our home at
Carlsberg in connection with the first distribution of a legacy for theencouragement of a young student or artist, which carries Christian'sname and which is founded by his old aunt and schoolmistress, Hanna
Adler, whom you will perhaps remember.

4
9

On this occasion I tried in a few words to express our deep
thankfulness for the testimonies of faithfulness to the memory of
Christian, of which the vases from Japan is one of the most touching・They stood with red chrysanthemums under his picture which a closefriend of us, a distinguished Danish painter, who has shown Christiangreat friendship and understanding, has made after his death and which
in a wonderful way expresses the deep earnest which in spite of his
youth was characteristic for his whole attitude to life.
This picture hangs in my study at Carlsberg, and we think that thisplace, as long as his mother and I are alive, may perhaps also be thebest place for the memorial vases, as Christian in our lifetime has
found a resting place in the grave of my father, after whom he wasnamed, and we are not sure that there on this grave can be found a placequite fitted for the beautiful vases. Where they stand how, they will
every day remind us of a11 the kindness you and our other Japanese
friends showed Christian in his life and the faithfulness you showed him
after his death.
We ask you kindly to extend our deepfelt thanks to al1 the friends
who have contributed to this most treasured gift. We will soon write to
you all again and send copies of the memorial words and of the picturesof Christian. We also hope very much that you and other of our friends
will visit us again, and we are ourselves looking forward to visit yourcountry which has for many years taken so great parts in our thoughts.
It was with the greatest regret that we had to postpone this visit still
further, but we hope that you will understand that we felt it impossible
for us to leave the other children under these sad circumstances.
With our kindest remembrances and heartiest wishes to you all,Yours ever,Niels Bohr

50

Julen 1934
Dear Dr. Nishina!
I send you the best wishes for Christmas and the new year for you
and your whole family.
I ought to have written you a real letter

already long ago in reply to your last kind letter, but I shall do sosoon.
Only 工 must tel1 you that the beautiful vases you sent Prof.
Bohr, came through without our paying any duty at al1.

Otherwise I

should of course have paid it and written about it to you, as you asked
me to do. But this was the very e
a
s
!
i
.
e
s
t. They are beautiful and Prof.
Bohrs were much touched to get them and appreciate them very much.
Kindest regards and the best wishes for a happy new year
Yours
Betty Schultz

GL. CARLSBERG
VALBYFeb. 26 1935
Dear Dr. Nishina,
I send you herewith some copies of a memorial paper about our
beloved Christian.

The first part of it is the farewell, which myhusband said to Christian from us all, when he was carried away from
home, after having been brought to us from Sweden.
The second part
countains some words, which my husband said on Christian's birthday,
when the legacy,which Miss Adler has given to his memory, was given
away for the first time. The four portraits are reproductions after two
beautiful paintings, which Julius Paulsen and William Scharff have made

5
1

to us, they are both near friends of us and were both so fond of
Christian. The pictures are very like him, but the one of Paulsen has
lost more in reproduction than the one of Scharff.

Your two beautiful

vases are standing under the pictures of Scharff in my husband s study,
at present with a branch of a spiny bush in them.

I never look deeply

touched by the faithfulness and affection, which you have shown to
Christian and us in this beautiful way. It has been a very sad year for
us, and we have been so sorry, that we had to give up our journey toJapan this spring, but I think you will understand that it would be too
difficult for us to leave all the children alone under these sad
circumstances and too sad for us to begin this journey alone, we had
been planning it and talking so much about it with Christian. I hope tobe able to come with my husband and Hans, when they go in spring 1937,
it would be a great pleasure to see all our friends again and awonderful experience in our life to see your beautiful country. We havejust had a letter from Professor Langevin telling us about the wonderfultime he had in Japan. My husband has not been feeling quite well thiswinter, the deep sorrow besides all his work, has been too much for him.
He felt he had to take a holiday and is at present in Arosa together
with Hevesy, from there he goes to Bayern to spend some days skiing with
Heisenberg in the Bavarian Alps.

Hans is also going there, he left

yesterday morning to meet my husband in Munchen; it is Hans

first

j
ouney outside Scandinavia, he was very excited and happy. I hope thatyou are some day coming over here again, all your friends would be so
happy to see you and you must bring your wife too. Will you be so kindand forward the other papers, I am so sorry to trouble you but I havenot got the address.
With the best wishes to you and your family and heartiest
greetings,

hu

r

︐o
n
u

eh

V4
1 ゐe

rt

ee
c
r
nqd

Lr
s
a
M

v
a
r
e
v
s

E
U
O

Y

5
2

Copenhagen, 2/3 1935
Dear Dr. Nishina!
As Mrs. Bohr has told you in the enclosed letter, she sends copiesof the speech Prof.Bohr made by Christian s funeral to you and theother friends in Japan.

They are sent by the same post as printed

matter and Mrs.Bohr asks you to be kind enough to give them to theother gentlemen.

Prof. Bohr himself is at present in Germany, snow‑

skating together with Heisenberg, so I have enjoyed a quiet time thelast fortnight.

I hope you and your family are in good health and send

you the kindest regards
Yours sincerely
Betty Schultz

TOKYO, Jan. 8th. 1936.

The Institute of Physical andChemical Research.
Komagome, Hongo, Tokyo
Dear Professor and Mrs. Bohr,

工 amvery sorry that I have not answered to any of your letters,

which I have received in connexion with our beloved Christian during
past one year with much sorrow, sympathy

and gratitude.

The

accumulation of every day task in our Institute prevents me fromwriting
any letters except those for urgent matters. It is a very sad condition
which, however, I am unable to change at present.
The copy of Professor Bohr s memorial speeches on two different
occasions of Christian, which Mrs. Bohr very kindly sent to us all, gave
us a vivid picture of Christian himself, his family and surroundings. 工

5
3

was very much moved by reading it. Your very kind words on us Japanese
friends cannot be read without a deep gratitude. I shall keep the copy
forever in order to cherish the dear memory of our beloved Christian.
About three weeks ago, we seven Japanese physicists who stayed inyour Institute sent by parcel post a small ivory carving of a little
chicken coming out of an egg.

This is to express our sincere

congratulations on your fiftieth birthday. It is very late to send ourwishes at this time.

This has been caused among other different

circumstances by a great distance, which prevents us from obtaining
up‑to‑date informations of happenings in Copenhagen. I hope you will
excuse us for this unduly delay.
As regards the carving we meant it for the occasion, because it
expresses birth and it also symbolizes your entering into the new stageof your life.

With this small token we send you our heartiest wishes

for your health, prosperity and success in your future work as ever.
The inscription written in Japanese on the back of the stand may
roughly be translated as follows,
For the Celebration of Fiftieth Birthday,
To Professor Bohr,
October 7th.
, 1935,
From Shin ichi Aoyama, Kenjiro Kimura,
Yoshikatsu Sugiura, '
l
'
o
s
h
i
o Takamine,
Yoshio Nishina,Mitsuharu Fukuda
and Takeo Hori.
The names of the contributors are given in Japanese alphabetical order.
We are all looking forward to welcoming both of you and Hans here
in the spring of 1937 and hope that nothing will this time come in theway of the realisation of your long planned journey.

54With kindest regards and best wishes to yourself and your family
from my wife and myself,
Yours everY.
Nishina

Universitetets Institut
for Teoretisk Fysik

Blegdamsvej 15 K￠benhavn ￠February 8th 1936.

Dear Nishina,
I can hardly say, how great a pleasure you and our other Japanese
friends have given me by the most beautiful gift to my 50th birthday,
and how touched my wife and I were for your most friendly andsympathetic letter.

The ivory chicken stands by itself on a little

cupboard in the same room where the bronze vases stand under thepainting of Christian, reproduced at the end of the little memorial
pamphlet we sent you last year, and which dayly remind us of yourfaithful friendship.

The chicken is most admired by everybody, and I

appreciate myself also very much its fine symbolic meaning.
My wife and I look forward very much to come to Japan next year tomeet you all again and see ourselves your country, which in our thoughts
has always been surrounded with so much romance and beauty,and for Hans
too it will be a most wonderful adventure; he has developed into a big
boy now, of whomwe have already great support in many ways.

When hehas finished his school this summer, he will at any rate for the firstyear specialize in atomic physics and will surely be a great help to me
also in preparing the lectures which I shall be giving in Japan.
Just in this moment my wife and I are leaving for England for a few
weeks, where I shall speak in London about some new ideas regarding the55constitution of atomic nuclei which I have developed in the last mon七hs.
As soon as I come back 工 shall write and tell more about it and also
about the more detailed program for my lectures in Japan. To‑day I
wanted only to express my most hearty thanks to you and our otherJapanese friends and to send you all the kindest greetings and best
wishes frommy wife and myself.
Yours ever,Niels Bohr

d

n
a

o

− K

ly

a

SZ

c h 0−
・
LCT

F
EA

ya︐
heo
psqd
en

OH

fRO

S

−−

七 ha

︑
ec
ae
︐
t
u l m
tmo
eqd
円﹂ m

no
z
k

hu

T

e

TOKYO, April 23. 1936.

Dear Professor Bohr,I thank you very much indeed for your kind letter of the 8th.
February, which I received a long time ago. Meantime your paper on theconstitution of atomic nuclei, which you mentioned in your last letter
appeared in Nature and had a great influence on our view towards thenuclear phenomena. In my opinion your new theory brought us much nearer
to the solution of the nuclear problems than previous views, although
the theoretical treatment has become very difficult. I wonder how
theoretical physicists are going to attack the problem.

I am looking

forward to the joint paper of you and Kalckar, as was mentioned in yourpaper. I should like also to know about the later development of yourview.
As regards the program of your journey to Japan and of lectures tobe given next year， 工 should like to have your rough suggestion as thebasis of our considerations, because all depends on about how many
lectures you would like to give us and how long you would like to stay5
6

in this country.

As I often wrote to you, we should 1ike of course tohave you here as long as possible.

The sum of twenty thousand yen

including your total travelling expenses, which Professor Nagaoka
arranged to offer you in September 1934 is not changed, as I understand.
I hope that you would be able this time to realize this longplanned journey and we are all looking forward very much to seeing Mrs.
Bohr, Hans and yourself here in Tokyo.
With best wishes to you and your family frommy wife and myself.
Yours ever,Y.Nishina

The Institute of Physical andTOKYO,August 3, 1936.

Chemical Research.
Komagome, Hongo,Tokyo
Dear Professor Bohr,I thank you very much indeed for your kind and interesting letterof the 2nd. July, which gave us a great pleasure by informing us of thevisit to this country of yourself, Mrs. Bohr and Hans in April next.
Iam really pleased to hear that you are going to realise your longplanned journey.

We are all looking forward to seeing you and yourfamily here in Tokyo, and listening to your lectures and discussions,out of which we expect to profit very much.
I have told your intention to Professor Nagaoka and he is going toarrange the monetary matter.

As I understand, Professor Nagaoka istrying to get the fund from Mitsui and Mitsubishi, the two richestfamilies in this country.

He thinks that the matter will soon be57

settled anyhow.
I advice you therefore to proceed with yourpreparations for the journey under the assumption that the monetary
question has already been settled as mentioned in my previous letter.
工 see from your letter that the Conference held in your Institutelast June must have been very interesting indeed.

I saw its shortreport in Nature and 工 can imagine that there has been a great deal of
fruitful discussions. We are far away from centres of such discussions
and we hope to learn very much from you on such questions when you comehere.
I thank you for the reprints of your two papers, both of which we
discussed very much in our laboratory,when they came out. There were,
however, some points which we could not understand very wel1. You wil1
probably tell us about themwhen you come here next year.
In mylaboratory we

have

not

done

much

recentlyeithertheoretically or experimentally. At present 工 ammuch occupied with theconstruction of a cyclotron and a high tension installation as well asbuildings for housing them. We hope to start the cyclotron at the endof October.

The magnet,however, is 66 cm in diameter and 14,000 gaussin field strength and is not large enough. We are therefore now trying
to get a fund for constructing a larger magnet. It is very interesting
to see from your letter that you are also constructing a cyclotron as
well as a high tension installation.
I should 1ike in this connexion to ask you one question. In ourlaboratory we have been discussing very much whether we should build ahigh tension source or not.

The high tension which we can obtain bymeans of the Cockcroft method is l to 2 million volts or 3 millions at
the highest as will be done at Cambridge. The energy obtained by suchan installation is thus much less than that obtained by a cyclotron ofsay 66 cm in diameter and 17,000 gauss in field strength. Some of us
therefore maintain that we should abandon the construction of the hightension source and use the money instead for the magnet of the cyclotron

58

to be bui1t and increase its dia
meter, that wi11 be more useful. Someof us, however, contend on different grounds that we should construct
the high tension source of the Cockcroft type. The settlement of thismatter is very urgent in our case.
Now 工 see from your letter that you are going to build a cyclotron
as wel1 as a high tension source. 工 should like very much・to know forwhat purpose you are going to use the high tension source besides
cyclotron.

I know that you have not time for informing me of thismatter and I should be very much obliged to you, if you would let
somebody of your laboratory answer to my question.

It would help usvery much in solving our urgent problem.
工 shal1 stop here for to‑day. If you want to know anything about

your jouney to Japan,please do not hesitate to let me know. I shall dowhat I can.
With best wishes and kindesヒ regards to your family and yourself
from my wife and myself,
Yours everY.
Nishina
P.S. In connexion with your visit to this country, I expect that we
shal1 want your short biography on different occasions. I should bemuch obliged to you, if you would let me know where to find it.

5
9

Universitetets Institut

Blegdamsvej 15 K￠benhavn ￠for Teoretisk Fysik

January 16th 1937

Dear Dr. Nishina,
Mrs. Bohr told me that you wanted some information of Prof. Bohr,
before his arrives at Japan.

As we did not exactly know what

informations you wished, we send you enclosed an article, published in a
Danish biographical dictionary, hoping that you will still remember somuch of Danish language, that you can find the wanted informations fromthis article.
I hope that you and your family are in good health and send you thekindest regards.

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The Institute of Physical andTOKYO, Feb. 15, 1937.

Chemical Research.
Komagome, Hongo, Tokyo
Dear Miss Schultz,
工 thank you very much indeed for the biographical note of Professor

Bohr, which you very kindly sent to me. We want it in order to giveinformations to some authorities concerning Professor Bohr s career.
We are all looking forward to seeing Professor and Mrs. Bohr aswell as Hans, whom we expect here to arrive on the 15th. April. They
will bring us various news from Copenhagen.

60

I am very sorry that I have not written to you for so long a time.
For recent years 工 have been so busy everyday that I cannot write
letters except for inevitable things. This is a very deplorable stateof things but I cannot change it at present.
日ow are you getting on?

In the absence of Professor Bohr, have you

much time for yourself? Please let me hear from you now and then when
you have time.
With best regards and kindest remembrances
Yours sincerely
Y.Nishina

On board of Shanghai‑maru NYK.

Post card

May 20th. 1937
Dear Nishina
our minds and our hearts are so full of the wonderful days in Japanand the thoughts of our faithful Japanese friends, t:
1at I shal1 not try
to express our feeli珂 s and our tttanks in any such short way.
I wantonly to say that we feel that we are still in your remindful andbrotherly care ‑as your kind telegram so effectfully proved‑ and that
I therefore felt that I must tell you that.we have had a nice sea
journey and already are in sight of the Chinese coast.
With kindest regards and heartiest wishes to you all,yours everNiels Bohr

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ヤミ：~－I ：日記；~~立:1；以以： i,~;jj62August 17,1948
Professor Niels Bohr
Institute for Advanced Study
University of Princeton
Princeton, N.J.
U. S. A.

Dear Professor Bohr:As I heard that you are now staying at Princeton and Dr. Yukawa iscoming to the Institute for Advanced Study, I avail myself of thisopportunity for writing this letter to you.
It is really a long time since I wrote to you last. Do you remember
we saw you off at Nagasaki? A good deal has happened during these 10
years. How is your family?
Japan is not the same Japan which you saw in 1937. The trouble
began in Manchuria just after you had passed through that country.
Since then everything went in the wrong direction and at last we arehere in a devastated town in which poverty prevails i:lll over.
At the direction of GHQ here our Institute was reorganized into a
private concern in March last. I became the President and has to run
the Instutute, the administration of which is not an easy matter at thistime of national hardship. The most difficult thing is to finance theInstitute to which I have to concentrate my energy. I gave up physics
at least for some time to come and became an administrator and abusiness man. One cannot do what he wants to do. The present objectiveof our Institute is the application of science to peaceful industry in63order to promote the rehabilitation of general economy of this country,
in which the poverty paralyses its whole machinery.

Scientists musttake their due share in realizing the economical recovery of Japan inorder that she can assume her responsibility in promoting world peace.
I wish you and your family a good health and a good luck. Please
send my best regards to Mrs.Bohr.
With best personal wishes,

︐

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Komagome Bunkyo‑ku,Tokyo

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Blegdamsvej 15, Copenhagen
December 9, 1948.

Dear Nishina,
工 was very happy and moved to receive your letter which Yukawa

forwarded to me from Princeton and I need not say that the whole family
as well as your many old friends in the Institute were deeply interested
in having news from you.
My wife, Hans and I will never forget the days at Nagasaki where wetook leave from you and our other friends after the wonderful time we
had spent in Japan and which the faithful friendship of you all made not
only so pleasant, but also so enlightening an experience to us. Surely,
the troubles which already then caused you anxieties should soon change

64

everything, but we must now al1 look to the future and each in his own
way strive for a more hopeful development.

In spite of all present

divergencies I feel that the great and terrible lessons which al1
mankind have received cannot fail in urging such a cooperation between
all nations on which not only prospertity but the very survival ofcivilization depend.
I feel sure that you will be able in a most effective manner toassist in the recovery and stabilization of your country and that within
few years you can again continue the scientific researches with which
you and your group have had so great success.

In Princeton, where mywife and Aage and I stayed last spring, all the Institute learned withgreat admiration about the advances in the development of quantum
electrodynamics, which were made in Japan even in the times of greatestdifficulties and I just heard from Oppenheimer how happy they are forthe collaboration with Yukawa.
Here, we all are very busy with an extension.
of the Institute which
will allow us to widen the field of our present experimental researches,
although there is of course no question that we can extend these to thefields in which in U.S.
A. with such extraordinary resources new and mostpromising advances are being made. We hope, however, to be able again
to establish a smaller center for international cooperation in physics
and we have already had a number of visitors from other countries.
The reorganization of the Institute should be finished at the endof the coming year and, in the beginning of 1950, we plan to have ameeting where we hope to see as many as possible of the old friends who
worked here in earlier and more recent times. Especially we should be
able to dispose of means to cover your travelling expenses. As soon as
such arrangements are made I shall send you a formal invitation.
I can hardly say what a pleasure it would be to the whole family
and your many friends in Copenhagen to see you here again and how much I
myself will look forward to being able to talk with you about old days

65

and the new prospects in physics and not least about the general・
human
problems which are so deeply on the mind of us both.
My wife joins me in sending our heartiest greetings and warmest
wishes to yourself and all our Japanese friends.
Yours ever,Niels Bohr

Professor Niels Bohr

August 19, 1949

Universitetets Institut for Teoretisk Fysik
Blegdamsvej 15
Copenhagen, Denmark
Dear Bohr:
工 receivedyour kind and interesting letter of December 9, 1948, towhich I am very sorry not to have answered owing to my negligence. 'l'headministration businesses of our Institute, of the Science Council ofJapan, and of a number of governmental as well as private committees
absorb whole my time.
Now I am very pleased to tell you that I am coming to Copenhagen inorder to attend the meeting of International Council of ScientificUnions, as a delegate representing the Science Counci1 of Japan, of
which 工 amone of the Vice‑Presidents. I leave here on September 8 andshall probably arrive in Copenhagen on September 13 via London. Afterattending the meeting I shall leave Copenhagen on September 22. It is avery short stay but owing to the administration of my Institute 工 cannot
stay longer. It is the first time after the war that Japan sends anofficial delegate to such an international conference. I am looking
forward to seeing you and your family and all my old friends as well as66international figures in science.
I heard that my invitation was initiated by you and Fraser inParis. The Occupation Authority here in Tokyo received a letter ofenquiry from Dr. Stratton, asking whether a delegate can be sent fromJapan and adding that they will explore the possibility of defraying thecost of the travel. The GHQ authority replied in the affirmative about
4 weeks ago on the condition that my travel expense be paid by ICSU, butthey have not heard anything from Stratton.
Meanwhile there are a lot of procedures for me to take in order togo abroad. These・preparations are being now made and the GHQ will send
me to Copenhagen in any way.

This is the story how my visit to old

Copenhagen is going to be realized.
工t is already 21 years since I l
eft Copenhagen and I should be very
pleased to be able to talk to my old friends.

With best wishes to your family and yourself,
Yours ever,Y. Nishina

Professor Niels Bohr

August 26, 1949

Universitetets Institut for Theoretisk Fysik
Blegdamsvej 15
Copenhagen, Denmark
Dear Bohr:I should like just to tell you that Dr. Stratton wired to GHQ here
in Tokyo informing the impossibility of finding any external financial

67

aid for my travel. Meanwhile, howev
er,GHQ decided to bear the expenseand I shall leave Tokyo on September 8 arriving in Copenhagen on
September 13 via London by B.
O.
A.
C. plane as I wrote to you in myprevious letter.
At present I expect to leave Copenhagen on September 22 but there
may be a change in the schedule of plane route and also I may have toattend the General Assembly of UNESCO to be held from September 19. Inthat case I have to leave Copenhagen earlier.
Looking forward to seeing you again,
Yours ever,Y. Nishina

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October 8, 1949

Dear Professor and Mrs.Bohr:
It is just a week since 工 came home from my long journey, therecollectionofwhich gives me muchdelight, consolation

andencouragement. 工 was very, very glad to see you and your family again,
which I had never expected during the war to be possible and which 工 had
always wished to do since the end of the war. It was especially a greatjoy for me to see both of you are very well and have changed very little
after such strenuous years.

When I was talking with you at your home,

you always gave me an illusion that I had been at your home at
Blegdamsvej, forgetting the lapse of 21 years. At the same time, yourboys who have splendedly grown up and been doing very well and yourbeautiful mansion and extensive gardens brought me back to the reality

68

and made me think a great deal on what have happened during the intervalof these two decades.
It was very kind of you to have done for me to make me happy andpleasant in all possible ways for which I cannot be too thankful. The
talk with both of you gave me a great encouragement. The shopping on
Saturday is a happy remembrance. Those things are great contributions
to the living of my family.
Since I have been taken up by the General Meeting of the Science
Council of Japan, which lasted full four days, I have not yet been able
to see our Japanese friends, to whom you were very kind to give
beautiful presents.

My wife was very, very pleased to have those nicethings and asked me to send you many, many thanks.

In a few days I

shall see all of our friends in Tokyo and talk about you and your home.
I am sure they will all be very pleased.
At the General Meeting of the Science Council of Japan，工 made areport on the Copenhagen Meeting of !CSU.They were very pleased at thereturn of our country to a member of the international cooperation inscientific world. Our future contribution to such cooperation depends
on the effort of our scientists in respective fields. This has given abright hope and encouragement to Japanese men of science.
At your kind seeing me off, I left Copenhagen Monday morning,
September 19 and arrived in Paris the afternoon. I stayed with Frasers,
whom I got to know at Hamburg in 1927 ‑ 1928.

I visited the General

Assembly of UNESCO, which started on the same day and in which I had aninterest,because I am President of the Federation of UNESCO Cooperative
Associations in Japan, although Japan is not admitted yet as a memberof the organization.

I stayed two days in Paris and flew to London

Wednesday (September 21) and saw Dr. Stratton at Royal Empire Society.
On account of the delay in obtaining passport visas of Iraque, Siamand 工ndia, I lost my seat in the British Overseas A
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6
9

plane which left London Friday morning(
September 23). I had tochange
the plane from BOAC to PAA(
Pan American World Airways) in order toarrive in Tokyo as early as possible. 工 succeeded to obtain a seat in
the plane which left London Monday(Sept.26),but the reservation was only
up to Calcutta beyond which it was not possible at London to get
confirmation because of shortage of time. In spite of this uncertainty
工 left London Monday evening and arrived at Calcutta Wednesday(Sept.
28)

morning and could reserve a seat as far as Hongkong beyond which there
was again too little time to ascertain.
On leaving Calcutta Thursday night(Sept.29） 工 arrived at Hongkong
Friday afternoon(Sept.30) and found that I could keep my seat up toTokyo,where I arrived Saturday morning(Oct. 1). At Hongkong, while westayed for three hours at air port, my bag disappeared from the cabin.
The bag contained the beautiful elephant you gave me and I was very,very
sorry. But several days afterwards they found the bag in the lobby of a
Hongkong hotel and was safely returned to me in Tokyo. This might havebeen due to the lucky elephant in the bag but 工 do not still understandhow the bag crossed the Hongkong custom barrier.
In London 工 sawthe news of the Russian atomic bomb, which aroused
a great excitement. In Tokyo people talk much about it. I hope aneffective method of international control of atomic energy will soon beestablished.

A resolution for its request was passed by the General

Meeting of the Science Council of Japan.
On my ways to and from Copenhagen, I had a chance of observing
various civilizations and standards of living, which are closely
connected with economies of respective communities, one of the mostimportant international problems. 工t seems to me that the solution ofthis difficult question demands a close international cooperation basedonscientificinvestigationsofnaturalresources,industries,

population, traditions and histories of all localities. This is a very
hard task but it has got to be done sooner or later, if mankind want tohave a rational existence.

70

Please send my remembrances to Hans, Erik, Ernest and their family.
I had no time at Paris to call up Erik, to whom I should like to write
soon.
With best thanks and warmest wishes,
Yours ever,Y.Nishina

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