Popular Science Monthly/Volume 41/August 1892/Sketch of John Couch Adams
|SKETCH OF JOHN COUCH ADAMS.|
ONE of the most striking illustrations of the value and range of man's reasoning faculty is afforded by the substantially simultaneous calculation, on a purely mathematical basis, of the elements of the then unseen and unknown planet Neptune, and the prediction of the place in the sky where it would be found on a given day, by the Englishman Adams and the Frenchman Leverrier. While Leverrier succeeded in first attracting public attention to his work, Adams anticipated him in beginning the calculation and in bringing it to a satisfactory result.
Prof. J. W. S. Glaisher treats Adams's first paper, by means of which the new planet might have been discovered, as furnishing the final and inexorable proof of Newton's law of gravitation; and the day when it was taken to Greenwich—October 21, 1845—as therefore marking a distinct epoch in the history of gravitational astronomy.
John Couch Adams was born at Lancast, seven miles west of Launceston, Cornwall, England, June 5, 1819, and died at the observatory in Cambridge, January 21, 1892. His father was a tenant farmer; his mother had a small landed estate of her own, and had inherited her uncle's library, in which were a few books on astronomy. He was interested in these books, and made rapid progress at the village school, and was learning algebra before he was twelve years old, at which age he went to a private school at Devonport, where he had Mr. Grylls, a cousin of his mother's, as his teacher. While he studied, as usual, the classics and mathematics, astronomy was his favorite branch, and he was making notes and drawing maps of the constellations when fourteen years old; he read eagerly all the astronomical books he could find, and soon became interested, by the perusal of Vince's Fluxions, in the higher mathematics. In 1837 it was contemplated to send him to the University of Cambridge; in October, 1839, he entered St. John's College of that university. During his undergraduate career, according to Prof. J. W. L. Glaisher, he was invariably the first man of his year in the college examinations. In 1843 he was graduated as senior wrangler, being also first Smith's prize-man. The occurrence of a small constellation of mathematical senior wranglers at Cambridge about this time is noted in one of the biographies of Adams, viz.: Stokes in 1841, Cayley in 1842, and Adams in 1843—all three of whom have since been professors, and famous. Adams was elected a Fellow of his college on the year of his graduation, and continued in that relation till 1852, when, he not having taken holy orders, his fellowship expired. In the next year he was elected to a fellowship in Pembroke College.
It was while still an undergraduate that Adams began the investigation of the irregularities of Uranus, that culminated in the discovery of the new, remote planet Neptune. The possibility of the existence of such a planet, acting upon the motions of Uranus, had been suggested by Bouvard in 1821. Mr. Adams's attention was drawn to the subject, according to Prof. Glaisher, by reading Airy's report upon recent progress in astronomy in the British Association volume for 1832-33. On July 3, 1841, at the beginning of his second long vacation, when he was in his twenty-third year, he made the memorandum, "Formed a design at the beginning of this week of investigating, as soon as possible after taking my degree, the irregularities in the motion of Uranus which are yet unaccounted for; in order to find whether they may be attributed to the action of an undiscovered planet beyond it; and, if possible, thence to determine the elements of its orbit, etc., approximately, which would probably lead to its discovery."
Prof. Glaisher further relates the history of the calculations: "In 1843, the year in which he took his degree, he attempted a first rough solution of the problem, on the assumption that the orbit was a circle with a radius equal to twice the mean distance of Uranus from the sun. The result showed that a good general agreement between theory and observation might be obtained. In order to make the data employed more complete, application was made, through Prof. Challis, to the astronomer royal, for the results of the Greenwich observations of Uranus. When they were obtained, Adams undertook a new solution of the problem, taking into account the most important terms depending on the first power of the eccentricity of the orbit of the supposed disturbing planet, but retaining the same assumption as before with respect to the mean distance. In September, 1845, he communicated to Prof. Challis the values which he had obtained for the mass, heliocentric longitude, and elements of the orbit of the assumed planet. The same results, slightly corrected, he took with him to the Royal Observatory, Greenwich, on October 21, 1845. The paper which he left at the observatory on this occasion also contained a list of the residual errors of the mean longitude of Uranus, after taking account of the disturbing effect of the new planet, at dates extending from 1690 to 1840." Prof. Challis began the search for the planet on July 29, 1846, three weeks before it was in opposition, and continued the observations for two months. His plan was to sweep a zone covering the computed place of the body, and extending over 30° of longitude and 10° of latitude. "For the first few nights the telescope was directed to that part of the zone in the immediate neighborhood of the place indicated by theory. Unfortunately, the observations were not immediately compared with each other, or Prof. Challis would have discovered, what he afterward found to be the case, that he had actually seen the planet on August 4th and August 12th, the third and fourth nights of observation.... On September 3, 1846, Adams communicated to the astronomer royal a new solution of the problem, supposing the mean distance of the planet as originally assumed, to be diminished by about the thirtieth part. The result of this change was to produce a better agreement between the theory and the later observations, and to give a smaller and therefore a more probable value of the eccentricity."
Leverrier's first paper relative to the subject was presented to the French Academy on November 10, 1845, and concerned the perturbations of Uranus produced by Jupiter and Saturn; but in it he also pointed to irregularities which could not be accounted for by the existing theory. In his second paper, June 1, 1846, he expressed the conclusion that the unexplained irregularities were due to an undiscovered planet exterior to Uranus. He calculated the longitude, but did not give the elements of the orbit of the disturbing planet. The place assigned by him to the supposed body differed by only one degree from that given by Adams in the paper which he had left at the Greenwich Observatory seven months earlier.
"Adams's researches," says Prof. Glaisher, "therefore preceded Leverrier's by a considerable interval; and in spite of the delay in carrying out the search, it had been carried on at Cambridge for nearly two months before the planet was found at Berlin. Adams's investigation may be regarded as having been completed on October 21, 1845, when he left his paper at the Royal Observatory. This was three weeks before Leverrier's memoir, showing that the irregularities could not be attributed to any of the known planets, was presented to the French Academy, and more than seven months before the presentation of Leverrier's second memoir. It is to be noticed that in this second memoir Leverrier did not give the elements of the orbit or the mass of the planet, which were contained in Adams's paper of October 21st."
A bitter controversy ensued over the question of priority in discovery, in which Mr. Adams took no part. He felt and expressed a warm appreciation for Leverrier; met him with great pleasure at Oxford in 1847; and was visited by him in the same year at Cambridge. A story was told of him for the first time by Dr. Donald MacAlister at the commemorative meeting at St. John's College, February 20, 1892, to the effect that several years ago, when a memorial volume was prepared to be presented to M. Pasteur as a testimonial of the appreciation of English men of science for his labors, Prof. Adams subscribed bis name, writing beneath it the motto, "Hommage au compatriote de Leverrier."
The small number and volume of Prof. Adams's publications, after his calculations for the planet Neptune, have been remarked upon. He was, however, an industrious worker, calculating in every quarter of the mathematical field and in mathematical astronomy, and is said to have left a large mass of manuscript work, much of which is expected to prove valuable. The Adams prize, of about four hundred dollars a year, to be awarded every two years to the author of the best essay on some subject of pure mathematics, astronomy, or other branch of natural philosophy, was instituted by members of St. John's College soon after the discovery of Neptune, as a testimonial to the honor conferred on the college and the university by the investigation. In 1848 Mr. Adams began the determination of the constants in Gauss's theory of terrestrial magnetism. He resumed the work and was occupied with it in the later years of his life, but had not completed it at the time of his death. In 1852, having been elected in the previous year President of the Royal Astronomical Society for two years, he communicated to the society new tables of the moon's parallax, to be substituted for those of Burckhart. These tables were printed in the appendix to the Nautical Almanac for 1856.
His memoir explaining the secular variation of the moon's mean motion was communicated to the Royal Society in 1853. The problem baffled solution. The French Academy had at different times given prizes for explanations to Euler and Lagrange, but neither of these mathematicians had been able to discover any secular term; and Euler, considering it established that such a term could not be produced by the principles of gravitation, had recourse to the supposition of a resisting medium. Laplace announced in 1787, as the true cause of the phenomenon, the gradual diminution in the mean action of the sun produced by the secular variation of the eccentricity of the earth's orbit. Theories were also proposed by Damoiseau and Plana, agreeing in principle with Laplace's, but differing slightly in the numerical values assigned to the acceleration. Adams found that Laplace's explanation of the phenomena was essentially incomplete, and suggested corrections to all the theories. Some controversy ensued, at the end of which Prof. Adams was sustained. A calculation of the same problem, made by Prof. Airy in 1880, was also corrected by Prof. Adams.
Mr. Adams was appointed, in the fall of 1858, Professor of Mathematics in the University of St. Andrews, where he continued his lectures till the end of the session, in May, 1859; and late in 1858 he was made Lowndean Professor of Astronomy and Geometry at Cambridge. He held the last position till his death. A part of his work in it was to lecture during one term in each year, generally on the lunar theory, but sometimes on the theory of Jupiter's satellites or the figure of the earth.
In 1867 he published an account of the results he had obtained with respect to the orbit of the November meteors, in the investigation of which he had co-operated with Prof. H. A. Newton, using the data and observations furnished by him. These calculations took notice of all the perceptible effects produced by the planets, and established the correctness of the period of thirty-three and a quarter years for the revolution of the meteoric body. In order to obtain a sufficient degree of approximation, it was necessary to break up the orbit of the meteors into several different parts, for each of which separate calculations had to be made. Prof. Adams afterward subdivided certain parts of the orbit of the meteors into still smaller portions, with a view of obtaining a closer approximation. The calculations on this subject have not been published, but they exist among his papers, and seem to be fairly complete.
A paper communicated to the Astronomical Society, in November, 1877, embodied a review of a memoir by Mr. G. W. Hill, of Washington, on the part of the motion of the moon's perigee, which is a function of the mean motions of the sun and moon. This paper is pronounced by Prof. Glaisher peculiarly interesting, because in it the author expresses his own views with respect to the mathematical treatment of the theory of the moon's motion. He seems to have preferred to treat the subject by its special problems; while he had great admiration for Delaunay's general theory.
Prof. Adams also paid much attention to pure mathematics, and treated many abstruse problems in a highly technical manner, in papers the very titles of which are an unknown language to all but accomplished mathematicians.
A large mass of papers which Sir Isaac Newton had left at his death, having been left to the University of Cambridge by Lord Portsmouth, it became Prof. Adams's task to arrange and catalogue the mathematical part of the collection. The work lasted many years, but proved very interesting to Prof. Adams, by casting light on the methods by which Newton had worked out his results.
On the resignation by Prof. Challis of the directorship of the observatory at Cambridge in 1861, Prof. Adams was appointed to succeed him, while he still continued in the Lowndean professorship. In 1870 the observatory began to co-operate in the scheme of the Astronomische Gesellschaft for the observation of all the fixed stars in the northern hemisphere down to the ninth magnitude, the observations being put under the charge of the first assistant, Mr. Graham. The zone assigned to the observatory was that between 25° and 30° of north declination. As related to this work, Prof. Adams gave, in an appendix to one of the volumes of the Cambridge Observations, the formulae and instructions which he had drawn up many years before for the formation of a proposed new fundamental catalogue, together with the mean places of the eighty-four fundamental stars from 1830 to 1870.
Prof. Adams was President of the Royal Astronomical Society in 1851-1853, and in 1874-1876, and had the honor of delivering the addresses in presenting the gold medal to Dr. Peters, Dr. Hind, D'Arrest, and Leverrier. In 1870, as vice-president, he delivered the address on the presentation of the medal to Delaunay. He himself received the medal in 1866 for his contributions to the development of the lunar theory. He received the Copley medal of the Royal Society in 1848. In 1881 he declined an offer of the position of astronomer royal. In 1884 he was one of the British delegates to the International Prime Meridian Conference, which met in Washington. He received honorary degrees from Oxford, Dublin, Edinburgh, the University of Bologna, and his own university; and he was a correspondent of numerous foreign learned societies.
Among his peculiar tastes in work Prof. Glaisher mentions the enjoyment he took in making calculations that called for long lines of figures, as illustrated in his calculation of Euler's constant to 263, and of some logarithms to 273, places of decimals. Few of his papers were produced spontaneously. In the majority of cases he was induced to give an account of some investigation of his own by the publication of a paper by some one else in which the same subject was treated. He was able to map out beforehand in his head the whole course of an investigation; and he rarely began to write till he had carefully thought out his subject, when he wrote straight on without interruption.
While astronomy and mathematics were his professed studies, he was interested in other branches of knowledge, was a man of most extensive general reading, was much attracted to special pursuits, and made a valuable collection of early printed books. His moral and intellectual qualities were well balanced.
Prof. Adams was attacked by a severe illness in October, 1889, but recovered and continued his mathematical work for several months. He was again attacked in June, 1890, by an illness from which he never fully recovered.