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SIMON NEWCOMB (1835-1909), American astronomer, was born in Wallace, Nova Scotia, on the 12th of March 1835. He became a resident of the United States in 1853, and graduated. at the Lawrence Scientific School of Harvard University in 1858,. having paid special attention to mathematics and astronomy. He assisted in the preparation of the American Nautical Almanac for 1857. In 1861 he became professor of mathematics in the United States navy, and was put in charge of the great 26-in. equatorial erected at Washington Observatory in 1873. In 1877 he was appointed director 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 Washingtion. 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, ard the unity of purpose which guided him throughout, Simon Newcomb must be considered as 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 treatment 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 assuming the directorship of the Nautical Almanac 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. Accordingly 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 astronomy," but the gigantic task which Newcomb laid out for himself, and which he carried on for more than twenty 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 completely adopted for use in the nautical almanacs. of all countries. A valuable summary of a considerable part of this work, containing an account of the methods adopted, the materials employed, and the resulting values of the various quantities involved, was published in 1895, as a supplement to the American Ephemeris for 1897, entitled The Elements of the Four Inner Planets and the Fundamental Constants of Astronomy. In 1866 Newcomb had published' an important memoir on the orbit of Neptune, which was followed in 1873 by a similar investigation of the orbit of Uranus. 2 About twentyfive years later the tables of these planets were revised by him in view of all the observations which had accumulated in the meanwhile at Washington, Greenwich, Paris and Cambridge. 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 Almanac office, and thus was ' Smithsonian Contributions to Knowledge, vol. xv.

2 Ibid. vol. xix.

completed one important section of the work projected by Newcomb in 1877.

Among Newcomb's most notable achievements are his researches in connexion with the theory of the moon's motion. His first work on this abstruse subject, entitled T heorie des perturbations de la lune, qui sont dues a faction des planetes,1 is remarkable for the boldness of its conception, and constitutes an important 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 unfounded, 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. In an elaborate memoir 2 he showed that the ancient solar eclipses described by Herodotus, Thucydides, and others, which seemed to require an increased value of the secular acceleration of the moon's mean motion to bring them into line with modern results, might safely be neglected, the ambiguity of the accounts in each case rendering uncertain either the totality of the eclipse or the place from which it was visible. In his investigation he employed the eclipses of the moon recorded in the Almagest, the Arabian eclipses between A.D. 800 and 1004, extracted from Caussin's translation of Ibn Junis, the eclipses and occultations of Bullialdus, Gassendi, and Hevelius, of the French astronomers at Paris and St Petersburg, and of Flamsteed at Greenwich, and deduced a secular acceleration of 8.8", agreeing well with the theoretical value.

On taking charge of the 26-in. 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, being of opinion that it was better to do one thing well than many things indifferently. The results of these skilfully conducted observations were published in a memoir on The Uranian and Neptunian Systems. 3 From this research it appears that the orbits of all four satellites of Uranus are sensibly circular, and although no special search was made, he concludes that none of Sir William Herschel's supposed outer satellites can have any real existence. From the motion of the satellites he finds that the mass of Uranus is - T - A o o th of that of the sun, while for the planet Neptune he finds a mass equal to 19 Toth of the sun, agreeing with the value previously found by him from the perturbations of Uranus within o th of its amount. As early as 1860 Newcomb communicated an important memoir to the American Academy, 4 On the Secular Variations and Mutual Relation of the Orbits of the Asteroids, in which he discussed the two principal hypotheses to account for the origin of these bodies - one, that they are the shattered fragments of a single planet (Olbers' hypothesis), the other, that they have been formed by the breaking up of a revolving ring of nebulous matter.

In the Astronomical Papers of the American Ephemeris will be found a large number of contributions from Newcomb's pen on some fundamental and most important questions of astronomy. Among these are papers on The Recurrence of Solar Eclipses, A Transformation of Hansen's Lunar Theory, Development of the Perturbative Function and its Derivatives. His memoir On the Motion of Hyperion, a New Case in Celestial Mechanics, is in some respects one of his most original researches. He discussed the transits of Venus of 1761 and 1769, and those of Mercury from 1677 to 1881. At the international conference, which met at Paris in 1896 for the purpose of elaborating a common system of constants and fundamental stars to be employed in the various national ephemerides, Newcomb took a leading part, and at its suggestion undertook the task of determining a definite value of the constant of precession, and of 1 Lionville, t. xvi. (1871), pp. 1-45.

Washington Observations, 1875, Appendix II.

3 Ibid., 1873, Appendix I.

4 Memoirs Amer. Acad. of Arts and Sciences, v. 124-152.

compiling a new catalogue of standard stars. The results of these investigations were published in 1899, 5 and have been in use since the beginning of Igo'. In the intervals of these immense labours, on which his reputation as an astronomer rests, he found leisure for works of a lighter character, e.g. his Popular Astronomy (1878) which has been translated into German, Russian, Norwegian, Czech, Dutch and Japanese, his Astronomy for Schools and Colleges (1880), written in conjunction with Professor E. S. Holden, and Astronomy for Everybody (1903). After his retirement from official life he published an excellent popular treatise on The Stars (1901). A more recondite work is his Compendium of Spherical Astronomy (1906). He also wrote on questions of finance and economics.

He received the honorary degrees of D.C.L. Oxford, and Sc. D. Cambridge and Dublin. In 1872 he was elected an associate of the Royal Astronomical Society, receiving its gold medal in 1874. In 1877 he was elected a foreign member of the Royal Society, which in 1890 awarded him the Copley medal. He also received the first Bruce medal of the Astronomical Society of the Pacific, awarded by the directors of the Berlin, Greenwich, Harvard, Lick, Paris and Yerkes observatories. Except Benjamin Franklin he was the only American to become an Associate of the French Institute. He died at Washington on the 11th of July 1909, and was given a military funeral, having been made a rear-admiral by Act of Congress in 1906.

An autobiography, Reminiscences of an Astronomer, appeared in 2903; and a bibliography of his writings is given by Mr Archibald in the Trans. Roy. Soc. Canada, XI. iii. 79. See also the obituary notice by H. H. Turner in the Mon. Not. R.A.S. (Feb. 1910), p. 305.