# Lectures on Ten British Physicists of the Nineteenth Century/Lecture 8

SIR GEORGE BIDDELL AIRY
(1801-1892)
George Biddell Airy was born at Alnwick in Northumberland on the 27th of July, 1801. His father, William Airy, was collector of the Excise duties for that district; his mother, Anna Biddell Airy, was the daughter of George Biddell, a well-to-do farmer in Suffolk. In 1810 William Airy was transferred to the county of Essex, and the family then settled in Colchester, the county town. Here George was first sent to a private school, where he got a good introduction to elementary mathematics; afterwards he was sent to the grammar school where he was initiated in Latin and Greek to the extent of being able to write Latin prose. He also got the usual instruction in Latin verse, but he did not excel in that kind of composition. On one occasion his father brought him a present from London, which had much influence on his future career—a terrestrial and a celestial globe. From this event he dated his interest in astronomy. Arthur Biddell, his mother's brother, lived on a farm at Playford, in Suffolk, and was a man of some scientific and literary culture, besides being interested in historical and antiquarian matters. George spent his holidays in this uncle's company and especially in his library; from this source originated an interest in mechanics, optics, poetry and antiquities. There he found the means of constructing a telescope for himself.
At school he distinguished himself, especially in memory work. Although not wanting in courage, he did not take an interest in athletic sports. It was the custom for each boy once a week to repeat a number of lines of Latin or Greek ​poetry, the number depending very much on his own choice. Airy repeated 100 lines every week; on one occasion he repeated more than 2000 lines. The schoolmaster was impressed with his powers and suggested to his father that the boy should be sent to Cambridge; who, on inquiry, concluded that the expense was too great for his straitened circumstances. However, the uncle took up the problem, and with the help of a Cambridge alumnus got the boy prepared in classics and mathematics for the entrance examination to Trinity College. In these preliminary examinations he acquitted himself so well, that a reputation for scholarship preceded his going there to reside. In 1819, when 18 years old, he commenced residence as a sizar of Trinity College. By a sizar is meant a poor student who is exempted from some of the expenses—he does not pay for dinner in hall; the sizars dine after all the rest, on the remains of the Fellows' dinner. Newton himself started in that same college as a sizar. George Peacock, who was then a mathematical tutor of the college, became his warm friend and adviser; he gave him a copy of Lacroix's Differential Calculus, translated by himself, Babbage, and Herschel, and also a copy of his Collection of Examples. At this time the Differential Calculus was beginning to prevail over Fluxions; Airy had got instruction in the old method, but he took to the new with great industry. At a breakfast party at Peacock's he met Whewell, who was a resident fellow graduate of the University.
Airy employed part of his first vacation in writing out a paper on the geometrical interpretation of ${\sqrt {-1}}$. He got the suggestion of "perpendicular" from some book; the aim of his essay was to apply that theory. Peacock to whom he showed the essay was much pleased. Mr. Hustler, his tutor, on the contrary disapproved of his employing his time on such speculations. The former was a philosopher and reformer, the latter an official and disposed to consider everything that is, is right. Airy however, whether by the influence of Hustler or otherwise, did not go very deep into the subject. He afterwards wrote: "I have not the smallest confidence in any result which is essentially obtained by the use of imaginary ​symbols. I am very glad to use them as conveniently indicating a conclusion which it may afterwards be possible to obtain by strictly logical methods; but until these logical methods shall have been discovered, I regard the result as requiring further demonstration." Here-we note a want of confidence in mathematical deduction which appears to have been characteristic of Airy and his generation of mathematicians.
In his first year Airy read Whewell's textbook on Mechanics, just published, the first innovation made in the Cambridge system of Physical Science for many years, and which made partial use of the differential notation (d). By the beginning of his second year he was so far advanced that he took two private pupils for instruction in mathematics—men of his own year. By this means he became able to defray all his expenses without help from his relatives. In his early career as a student he started the custom of keeping on his desk a quire of scribbling paper sewed together; and on the current quire everything was written—translations from the Greek, prose translations into Latin, mathematical problems, memoranda of every kind. These quires were carefully preserved. This habit of writing out everything made him an accurate and ready man, and placed him far ahead of his contemporaries in the college examinations. He adopted the rule of writing on his quire every day a translation into Latin of three or four sentences; this he did in preparation for the final University examinations. While he was an undergraduate Babbage's difference machine was much talked of: in his last undergraduate year (1822) Airy studied the subject and made a sketch of a computing machine. About the same time he prepared a paper on the construction of a reflecting telescope with silvered glass; a paper which brought him an introduction to Mr. (afterwards) Sir John Herschel, and Mr. (afterwards) Sir James South, two of the active astronomers of the day.
In Airy's time a candidate for B. A. was required to pass a University ordeal, which was a survival of the ancient system of examination. The candidate at the end of his second and third years was required to state three theses which he was ​prepared to defend in Latin against as many opponents. For instance Airy submitted the following theses:
(1) Recte statuit Newtonus in Principiis suis Mathematicis, libro primo, sectione undecima.
(2) Recte statuit Woodius de Iride.
(3) Recte statuit Paleius de Obligationibus.
An apponent was appointed to attack each thesis. The discussion was carried in the Latin language under the direction of a Moderator; and when the high men were engaged, the spectacle was sufficiently interesting to draw a great crowd of undergraduates. The statutes framed in the time of Queen Elizabeth, required that a candidate should keep a certain number of such acts; at this time all excepting the two mentioned were gone through as a matter of form. Airy's practice in Latin enabled him to acquit himself with high distinction. A few years later the respondent and opponents reduced the procedure to a farce by concocting their arguments beforehand, and the system was suppressed in 1830. This procedure explains the term wrangler and senior wrangler; the contest was originally a wrangle in the Latin language. In Airy's time there was a further tripos examination conducted partly in writing, partly viva voce in English. Airy came out Senior Wrangler, very far ahead of the next man. The year before Peacock had introduced a paper of questions entirely on the Differential Calculus, a procedure which definitely established the study of the continental mathematics at Cambridge University.
After graduating as B.A., Airy continued to read for the fellowship examination, and to take pupils, generally four in number. He was now elected a member of the Cambridge Philosophical Society. During the vacation he went on a geological tour in Derbyshire, visiting among other places Edensor, near Chatsworth, the principal residence of the Duke of Devonshire. His introduction was to the rector, the Rev. Richard Smith, a Cambridge man; he fell in love with the eldest daughter, and within two days proposed an engagement to marriage. This was before he entered the competition for fellowship, and in view of the rules then in force about the ​tenure of fellowship, was a rather bold step. No engagement was then made. In 1824 he was elected a fellow of his college. He also obtained the post of assistant mathematical tutor, and in addition took some private' pupils. While engaged in this work he prepared a volume called Mathematical Tracts, on subjects which were either deficient at the University, or else not presented in readable form, namely, Lunar Theory, Figure of the Earth, Precession and Nutation, and the Calculus of Variations. The volume was printed by the University Press, and brought its author both reputation and some money. This book, published in 1826, applied the continental notation of the calculus and it exerted a great influence on the study of mathematical physics at Cambridge.
Whewell was senior to Airy in academic standing by seven years. In 1826 they made experiments on gravity in the Dolcoath mine in Cornwall. One pendulum was swung at the top of the mine, the other at the bottom. After numerous observations of their periods in these positions, the one down below was sent up to be compared with the other at the top; when it emerged at the top, the experimenters were surprised and mortified to find the basket on fire, and hence the observations had to be abandoned. This same year the Lucasian professorship of mathematics fell vacant; a Head of one of the colleges sought to capture it as a sinecure; Charles Babbage, who had taken only a poll degree at Cambridge, also applied; and so did Airy. Babbage and the Head mutually destroyed one another, with the result that Airy was elected. Airy improved his academic standing, but not his income; the salary was only £100, and the position involved the giving up of some tuition work. He was not yet in a position to sacrifice his fellowship by marriage. He immediately issued a printed notice that he would give professional lectures in-the next term. There had been no lectures on Experimental Philosophy (Mechanics, Hydrostatics, Optics) for many years. The University in general looked with great satisfaction on such vigorous reform; but there were difficulties to surmount; no allotted term for the lectures, no allotted hour of the day, scarce any available ​lecture-room. In this contest Airy and Babbage first came into conflict.
It was the next year (1827) that Airy's path first intersected that of Hamilton. Dr. Brinkley, the professor of astronomy at Dublin had been made a bishop. Airy went over to Dublin to see about the appointment: finding that the electors desired to appoint W. R. Hamilton, although still an undergraduate, he retired. The following year the Plumian professorship of astronomy and experimental philosophy at Cambridge fell vacant, the salary of which was £300. Airy applied, and before he was elected took the extraordinary course of applying for an increase of salary. He was anxious to secure an income on which he could marry—a difficult thing in the constitution of the University. His good fortune did not fail him; he was elected and the salary raised to £500. He had now charge of the College Observatory, and a residence, to which two years later he brought Richarda Smith from Edensor. For eight years he lived and worked in the Cambridge Observatory. One of his first scientific works was a repetition along with Whewell of the pendulum experiments in the Dolcoath mine. Misfortune again attended the inquiry. A few days after the observations had been started, a mass of rock settled in the mine, stopping the pumps and allowing the water to accumulate; sufficient time was not left to complete the observations, and the result was again nugatory. After one year at the Observatory Airy began to publish his astronomical observations, first of all devising an orderly system of exhibition, then "quite a novelty in astronomical publications."
In 1832 a committee of the newly founded British Association asked Airy to prepare the report on Astronomy for the next meeting to be held at Oxford. This he did, and read part of it at the meeting. Mr. Vernon Harcourt, secretary of the Association, deprecated the tone of the report as relating to English astronomers; but Airy refused to alter a word. About this time Sir James South, the astronomer, on removing to a house in Kensington, bought a 12-inch achromatic telescope in Paris and employed Troughton & Simms of London to mount it ​equatoreally. South was not satisfied with the work, and refused to pay, and a lawsuit followed in which the English astronomers of the day were called on as expert witnesses. Airy and Sheepshanks were on the side of the contractors; Babbage on the side of South. The court appointed an arbitrator, who decided against South; whereupon he dismantled the telescope and issued the following notice:
OBSERVATORY, KENSINGTON
To shyock toymakers, smokejack makers, mock coin makers, etc. Several hundred weights of brass etc., being the metal of the great equatoreal instrument made for the Kensington Observatory by Messrs. Troughton & Simms, are to be sold by hand on the premises; the wooden polar axis of which, by the same artists, with its botchings cobbled up by their assistants, Mr. Airy and the Rev. R. Sheepshanks, was purchased by divers vendors of old clothes, and dealers in dead cows and horses, with the exception of a fragment of mahogany specially reserved at the request of several distinguished philosophers, on account of the great anxiety expressed by foreign astronomers to possess them, was converted into snuff boxes as a souvenir piquant of the state of the art of astronomical instrument making in England during the nineteenth century.
This dispute occasioned by one who eventually proved to be insane, led to much quarreling among the astronomical scientists of the day. De Morgan as a friend of Airy and Sheepshanks was publicly insulted by South, and on asking an explanation from him received what was virtually a challenge to a duel. Babbage, on the other hand, by his support of South, inflicted much damage on his own career. South, who was on the board of visitors, attacked Airy's administration of the observatory in public.
In 1835 Airy received an exceptional favor from the British Government; a pension of £300 was settled on his wife. Airy was a liberal, the Government conservative. No personal or political obligation was imposed; it was given avowedly as an encouragement to science. Later in this year a liberal Government came into power; they offered him the appointment of astronomer royal at the Greenwich Observatory, which ​at that time had fallen into a very inefficient state. He accepted and then they offered him Knighthood, which he declined on the ground of not being wealthy enough. When Airy took charge of the Cambridge Observatory, it had only one instrument—a transit instrument, and no assistant. By the date when he left for Greenwich the University had erected a Mural Circle and a small Equatoreal, and he had induced the Duke of Northumberland—a great patron of science—to purchase and erect what was then the finest equatoreal telescope in England.
At Greenwich Observatory Airy appointed two new assistants, and he speedily introduced his system of order. He introduced thirty printed skeleton forms for observations and computations; procured a copying press; punched four holes in papers and tied them flat in packets and subordinate packets. Later he got from a manufacturer a machine to punch the holes; and his system was an anticipation of the device which is now common in offices. All papers were carefully preserved in their proper place; and in his later years the ruling passion for order was so great, that he took more pains to classify a letter properly than to master its purport. About this time the difficulty of navigating iron ships was pressed on the Government; they asked Airy to make experiments on a ship. He made a series of observations, reduced them, and prepared magnets and iron correctors to neutralize the disturbance mechanically. He was successful in substituting mechanical for tabular correction; but the sluggishness of the large magnet of the compass remained a difficulty. Subsequently Sir William Thomson introduced instead of the large magnet a number of small magnets, and put a patent on it; but Airy got nothing from the Government for solving the main part of the problem. Being a very methodical man Airy kept a diary. Under September 15, 1842 he entered the following: "The Chancellor of the Exchequer asked my opinion on the utility of Babbage's calculating machine, and the propriety of expending further sums of money on it. I replied, entering fully into the matter, and giving my opinion that it was worthless." ​Fortified with this opinion, the Government broke off definitely with poor Babbage.
Airy's successor at the Cambridge Observatory was named Challis. In 1844 Prof. Challis introduced to Airy by letter the senior wrangler of the previous year named J. C. Adams, who in consequence of having read Airy's report on recent progress in astronomy to the British Association had several years before formed the design of investigating the unexplained irregularities in the motion of the planet Uranus, and who was now, his undergraduate years over, busily engaged on the solution. Adams wished to be furnished with the Greenwich observations of Uranus; these were promptly supplied. A year later Challis wrote a letter of introduction to Airy beginning: "My friend Mr. Adams, who will probably deliver this note to you, has completed his calculations respecting the perturbation of the orbit of Uranus by a supposed ulterior planet, and has arrived at results which he would be glad to communicate to. you, if you could spare him a few moments of your valuable time." Provided with this letter, Adams called at the Royal Observatory; Airy was absent in France. A month later, when Airy had returned, Adams called again; the astronomer royal was taking his midday walk, but would be back soon. Adams called an hour later; the astronomer was at dinner, and granted no interview. Adams left a paper giving the results of his investigation—the mass, position, and elements of the orbit of the new planet. A few days later Airy sent him a letter inquiring whether his theory likewise accounted for the irregularities in the radius-vector of Uranus. Adams did not reply; he felt mortified, and he thought the question trivial. Airy wrote no further letter to Adams; but a few months later, when Leverrier communicated similar results in a letter, he replied hailing Leverrier as the true predicter of the new planet. It was Airy's custom to turn off visitors without seeing them; interviews interfered too much with his pet order. He forgot his official position, and how he himself had been assisted. Adams was very unfortunate in the man to whom he confided his results. Prof. Challis made use of the Cam​bridge telescope to search for the planet; but he was anticipated by a Berlin astronomer who followed Leverrier's prediction. Challis actually mapped the planet as a star twice, but had not compared his maps. A great controversy arose; the attitude is neatly expressed by the couplet:
In the early forties there raged in England the "battle of the gauges." Of the railroads built some had adopted a broad gauge (6 feet), some a narrow gauge (4 feet 81/2 inches). The inconveniences of the diversity were beginning to be felt acutely, and the Government appointed a commission of which Airy was a member. The commissioners reported in favor of the universal use of the narrow gauge; their recommendation was opposed effectively in Parliament by the broad gauge interest, supported by Babbage, who devised very ingenious instruments and made much more scientific observations than Airy. However the narrow guage gradually became the solution of the difficulty. In the fall of 1848 Lord Rosse invited a number of astronomers to his castle at Parsonstown, Ireland, in order that they might inspect his large reflecting telescope. They were entertained for two weeks, Airy and Hamilton were the principal experts. Airy was able to remove a fault in the mounting of the great mirror, for in practical astronomy he was immensely superior to Hamilton; but as a calculator and scientific genius Hamilton was as much superior. It was on this occasion that Hamilton, influenced by Airy's sarcastic remarks, broke his abstinence resolution.
In 1851 Airy presided over the British Association, at the meeting held in Ipswich. The next year he communicated a paper to the Royal Society on the "Eclipses of Agathocles, Thales, and Xerxes." And he also lectured on the subject at the Royal Institution. In 1854 he renewed the attempt to determine by pendulum vibrations the intensity of gravity at the bottom of a mine; this time he chose the Harton coal mine in the north of England, and for his assistants observers ​from the different astronomical observatories of the country. The observations were successful; they gave the result that gravity is increased at the depth of 1260 feet by 1/19000th part: from which he estimated the density of the Earth to be 6.565. Airy not only supplied Hansen with the Greenwich observations of the Moon for the purpose of constructing his Lunar Tables, but he had them printed at the expense of the British Government and secured for him a personal grant of £1000 against the opposition of Babbage and South, who were on the Board of Visitors for the Observatory.
Airy came into conflict with Prof. Cayley about the kind of questions that ought to be set at the Cambridge Tripos Examination. Airy held that "The papers were utterly perverted by the insane love of problems, and by the foolish importance given to wholly useless parts of algebraical geometry. For the sake of these every physical subject and every useful application of pure mathematics was cut down or not mentioned." When invited to make an address at Cambridge, he seized the occasion to renew the attack; he also wrote to the board of mathematical studies. He wished to introduce into the list of subjects for examination Partial Differential Equations, Probabilities, Mechanics in a form which verges on practical application, Attractions, Figure of the Earth, Tides, Theory of Sound, Magnetism but not (for the present) Mathematical Electricity. In the correspondence which followed Cayley said, "I think that the course of mathematical study at the University is likely to be a better one if regulated with a view to the cultivation of science as if for its own sake, rather than directly upon consideration of what is educationally best (I mean that the best educational course will be so obtained) and that we have thus a justification for a thorough study of pure mathematics. In my own limited experience of examinations the fault which I find with the men is a want of analytical power, and that whatever else may have been in defect Pure Mathematics has certainly not been in excess." Later Airy criticized the questions set for the Smith prizes in 1879 in a letter addressed to the members of the Senate. He singled ​out the following question, "Using the term circle as extending to the case where the radius is a pure imaginary, it is required to construct the common chord of two circles." This drew forth from Cayley a rejoinder in which he gave a solution of the problem. To which Airy replied, "I am not so deeply plunged in the mists of impossibles as to appreciate fully your explanation in this instance, or to think that it is a good criterion for University candidates." The dispute ended in the introduction of mathematical physics into the course of study.
Airy was a liberal in religious attitude. He sympathized with the agitation which led to the abolition of religious tests for M.A. degree at the Universities of Oxford and Cambridge. He also supported. his fellow mathematician Colenso when he was attacked for his writings on the Pentateuch. With respect to Colenso he wrote, "He has given me a power of tracing out truth to a certain extent which I never could have obtained without him. And for this I am very grateful. As to the further employment of this power he and I use it to totally different purposes. But not the less do I say that I owe to him a new intellectual power." During the years 1872-3 Airy was president of the Royal Society. In 1872 he was knighted by Queen Victoria; he had declined the honor three times before. In 1873 he was consulted by Barlow and Bouch the engineers for the construction of a railway bridge across the Firth of Tay, on the subject of the wind pressure that should be allowed for. This bridge was blown down in 1879 with a passenger train on it, no one surviving to tell the tale. Airy's report was subsequently much referred to at the official inquiry: into the causes of the disaster.
In 1881 when 80 years old (20 years over the limit assigned by Osler for good work!) Airy resigned the office of astronomer royal and the Government, on account of his exceptional public services, granted him a pension almost equal to his salary. He died on the 2d of January, 1892 in the 91st year of his age. His life had been one of great activity; he was the author of eleven volumes and of 518 papers extending from 1822 to 1887. With regard to his habits while he was at Green​wich Observatory, he generally worked in his office from 9 to about 2:30, then took a walk, dined at about 3:30, and afterwards slept for about an hour. In the evening he worked in the same room with his family. "His powers of abstraction were remarkable; nothing seemed to disturb him, neither noise, singing nor miscellaneous conversation. . . . With his natural love of work and with the incessant calls upon him, he would soon have broken down, had it not been for his system of regular relaxation. Two or three times a year he took a holiday, generally a short run of a week or ten days in the spring, a month in the early autumn and about three weeks in the winter." Airy did valuable work and exerted great influence; especially we may look upon him as the founder at Cambridge of the modern school of mathematical physics.
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