NEWCOMB, SIMON (1835-1909), American astronomer, was born in Wallace, Nova Scotia, on March 12, 1835. He became a resident of the United States in 1853, and graduated at the Lawrence scientific school of Harvard university in 1858. He was an assistant in the American Nautical Almanac office 1857-61. In 1861 he became professor of mathematics in the United States navy, and was assigned to duty at the United States Naval Observatory. For more than ten years he worked with the various meridian instruments, and when the 26in. equa torial was erected in 1873 he was put in charge of that instru ment. In 1877 he was assigned to duty in charge of the American Nautical Almanac office, a post which he held until March 1897. In 1884 he became professor of mathematics and astronomy at the Johns Hopkins university, continuing, however, to reside at Washington. He was also editor of the American Journal of Mathematics for many years. In view of the wide extent and importance of his labours, the variety of subjects of which he treats, and the unity of purpose which guided him throughout, Simon Newcomb must be considered one of the most distinguished astronomers of his time. A study of his works reveals an unusual combination of skill and originality in the mathematical treat ment of many of the most difficult problems of astronomy, an unfailing patience and sagacity in dealing with immense masses of numerical results, and a talent for observation of the highest order. On taking charge of the Ndutical Almanac office, he became very strongly impressed with the diversity existing in the values of the elements and constants of astronomy adopted by different astronomers, and the injurious effect which it exercised on the precision and symmetry of much astronomical work. Accord ingly he resolved to "devote all the force which he could spare to the work of deriving improved values of the fundamental elements and embodying them in new tables of the celestial motions." The formation of the tables of a planet has been described by Cayley as "the culminating achievement of astron omy," but the gigantic task which Newcomb laid out for himself, and which he carried on for more than 20 years, was the building up, on an absolutely homogeneous basis, of the theory and tables of the whole planetary system. The results of these investigations have, for the most part, appeared in the Astronomical Papers of the American Ephemeris, and have been more or less com pletely adopted for use in the nautical almanacs of all countries. A valuable summary of a considerable part of this work was published in 1895, as The Elements of the Four Inner Planets and the Fundamental Constants of Astronomy. In 1866 New comb had published an important memoir on the orbit of Neptune, which was followed in 1873 by a similar investigation of the orbit of Uranus (Smithsonian Contributions to Knowledge, vols. xv. and
xix ). About 25 years later new tables of these planets were issued by him (Astronomical Papers of the American Ephemeris, vol. vii., pts. 3 and 4) based on unpublished investigations in which the elements were determined from the best available ob servations up to that time. In the meantime the theory of Jupiter and Saturn had been thoroughly worked out by G. W. Hill, Newcomb's distinguished collaborator in the Nautical Al manac office, and thus was completed one important section of the work projected by Newcomb in 1877.
Among Newcomb's most notable achievements are his re searches in connection with the theory of the moon's motion. His first work on this abstruse subject, entitled Theorie des pertur bations de la lime, qui sont dues a l'action des planetes, is remark able for the boldness of its conception, and constitutes an impor tant addition to celestial dynamics. For some years after the publication of Hansen's tables of the moon in 1857 it was generally believed that the theory of that body was at last complete, and that its motion could be predicted as accurately as that of the other heavenly bodies. Newcomb showed that this belief was un founded, and that as a matter of fact the moon was falling rapidly behind the tabular positions. With the view of examining this question, he undertook the reduction of every observation made before 1750 which appeared to be worthy of confidence. The results of this work were published in 1878. The discussion of the observations made after 1750 was interrupted by his work on the planetary tables carried on during his connection with the Nautical Almanac office. After his retirement from active service in the navy he was enabled, due to a grant from the Car negie Institution of Washington, to secure the necessary assistance from 1903 to 1909 to bring to completion the work of his great programme on the motion of the moon. This was finished less than a month before his death. The observations used in his work covered an extreme range in time of about 2,600 years and seemed, as he himself said, "to prove beyond serious doubt the actuality of the large unexplained fluctuations in the moon's mean motion." On taking charge of the 26in. equatorial at the United States Naval Observatory, Newcomb devoted it almost exclusively for the first two years to observations of the satellites of Uranus and Neptune. The results of these skilfully conducted observations were published in a memoir on The Uranian and Neptunian Systems.