10 SIMON NEWCOMB— CAMPBELL. tMBMOI TvoL. T xvn: 



his death. The monograph containing the results, published in 1913 as Volume IX, Part I, 

 pages 1-249, Astronomical Papers of the American Ephemeris and Nautical Almanac, is enti- 

 tled Researches on the Motion of the Moon, Part II. Part I had been published in 1878. New- 

 comb's final views concerning the lunar problems are summarized in his paper dated 1908, 

 December 11, entitled Fluctuations in the Moon's Mean Motion, in Monthly Notices R. A. S., 69, 

 164-169, 1909, from which we quote: 



With the aid of my assistant, Dr. Frank E. Ross, I have brought to a completion a study of the moon's mean motion 

 based on observations having an extreme range in time of about 2,600 years. The data of observation are as follows: 



1. The eclipses of the moon found in Ptolemy's Almagest, observed between B. C. 720 and A. D. 134. 



2. Observations of eclipses by the Arabian astronomers, extending from 829 to 1004. 



3. Observations of eclipses of the sun and of occultations of stars by the moon made by Gassendi, Hevelius, and 

 others, from 1620 to 1680. 



4. Observations of occultations of stars from 1C70 until the present time. 



The observations previous to 1750 were all worked up in my Researches on the Motion of the Moon, published in 

 1878. I have, however, subjected the results to a careful revision, and grouped them in a slightly different way from 

 the former one. From and after 1680 the observations are of a fair degree of precision, but there are frequent gaps 

 during the last half of the eighteenth century. The observations are fairly continuous since 1820. 



Taken in connection with the recent exhaustive researches of Brown, which seem to be complete in determining 

 with precision the action of every known mass of matter upon the moon, the present study seems to prove beyond 

 serious doubt the actuality of the large unexplained fluctuations in the moon's mean motion to which I have called 

 attention at various times during the past 40 years. * * * 



The feature of most interest is the great fluctuation with a period of between 250 and 300 years. I call this a fluctua- 

 tion rather than an inequality because, in the absence of any physical cause for its continuance, there is no reason to 

 suppose that it will continue in the future in accordance with the law followed in the past. * * * 



I regard these fluctuations as the most enigmatical phenomenon presented by the celestial motions, being so diffi- 

 cult to account for by the action of any known causes, that we can not but suspect them to arise from some action in 

 nature hitherto unknown. * * * 



One general result of the present state of things is that we can not draw any precise conclusions from a discussion 

 of the moon's motion in longitude, how refined soever we make it. For example, it is impossible to derive from obser- 

 vation the accurate coefficient of the 18.6-year nodal inequality in longitude, owing to the varying fluctuation. 



It is also not possible to predict the future motion of the moon with precision. If we require our ephemerides of 

 the moon's longitudes to be as exact as possible, we must correct the tabular mean longitude from time to time by 

 observations. 



It is not possible to give here an adequate impression of the immense labor involved in 

 carrying to completion the programs of lunar and planetary investigations referred to in the 

 preceding pages. In fact, a correct impression can not be gained even at the price of a careful 

 perusal of the voluminous papers describing the results unless the reader himself has dipped 

 into the complexities of gravitational astronomy and has had extensive experience in making 

 astronomical calculations. It means relatively little to say that the work was of herculean and 

 monumental proportions. Some of the investigations are described in the publications of the 

 United States Naval Observatory, in the various astronomical journals, and in special mediums; 

 but the theory and tables of the planetary and lunar motions are contained chiefly in the Astro- 

 nomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac, of 

 which eight and one-half large quarto volumes exist. These papers rank amongst the priceless 

 treasures of astronomical literature. 



G. W. Hill's theory of the motions of Jupiter and Saturn fills Volume IV, his tables for com- 

 puting the motions of these planets occupy the first half of Volume VII, and three extensive 

 papers by the same author are in other volumes of the series. Excepting, further, one paper by 

 Safford and two papers by Michelson (on the velocity of light), the remainder of the series is 

 made up of 25 extensive monographs by Newcomb. They treat of solar eclipses; of transits of 

 Mercury and Venus; of a determination of the velocity of light; of the theories of the motions of 

 Mercury, Venus, Earth, Mars, Uranus, and Neptune; of the constants of the orbits of these 

 planets, and tables to assist in computing their future positions; of the mass of Jupiter; of the 

 precession and nutation constants ; of the development of the perturbative function ; of the motion 

 of the moon, etc. Included also are Newcomb's Catalog of 1098 Standard Stars (their definitive 

 positions and proper motion), prepared to meet his own needs in reducing the already existing 



