394 ASTROMETRY 



both in form and content, to a definitely higher plane. Newcomb's 

 little book, Astronomical Constants, gives in concise and clear form 

 a bird's-eye view of the results of this work. Newcomb has succeeded 

 in attaining essentially what he started to attain; he has contributed 

 to science a homogeneous system of the fundamental constants of 

 astronomy; to his energy, almost bordering on the wonderful, we 

 are indebted for the realization of the most valuable results at present 

 attainable from modern observations. This view was expressed by 

 the Paris Congress of 1896, when it accepted Newcomb's system almost 

 unchanged; and if it were to assemble again to-day it would certainly 

 correct a small error which it committed. The determination of the 

 precession constant by means of the stars, which remained to be ac- 

 complished, as well as the formation of the fundamental catalogue of 

 stars, was delegated to him and was practically accepted in advance, 

 an evidence of the unlimited trust in the authority of Newcomb. 



Among the improved values of the masses which result from New- 

 comb's theory, I should like to call especial attention to the mass 

 of the planet Mercury, which is 30 to 40 per cent smaller than that 

 obtained by Leverrier. On account of the smallness of the coefficient 

 of the mass in the equations of condition, this is very difficult to 

 obtain. Now, however, it has been obtained in another manner and 

 independently, whence it arises that it may be considered as correct 

 within its probable error; this proves again the rigor with which the 

 calculations in the Astronomical Papers have been carried out. The 

 motion of the line of apsides of the planet Mercury, not explained 

 by theory, which was discovered by Leverrier, is confirmed by New- 

 comb. The explanation of this motion will have to wait for further 

 astronomical discovery. 



One of the most beautiful discoveries of the century was that of 

 the satellites of Mars. The new problem in celestial mechanics arising 

 therefrom was solved by the discoverer. The fifth satellite of Jupiter, 

 which was added to science by the distinguished observer, Professor 

 Barnard, has added another very important theoretical problem. If 

 we glance now over what has been presented, it cannot be denied 

 that celestial mechanics, during the past century, especially with 

 reference to the motions of the major planets, has essentially kept 

 pace with the results of observation, and that as a whole it satisfies 

 the enormously improved methods of observing. The last thirty 

 years of the past century belong, in this respect, to America, and 

 I believe that every European astronomer will agree with me that 

 they are also the most important. 



The progress made in the field of lunar theory has not been men- 

 tioned. To do this, however, I should have to explain the works of 

 Poisson, Plana, Hansen, Delaunay, Newcomb, Adams, Tisserand, 

 Hill, and many others, which would require an address at least as 



