ASTRONOMY 49 



"Traite de la Mecanique celeste," in five large volumes, 

 will always be one of the great classics in the domain 

 of mathematical astronomy. His Nebular Hypothesis 

 of the origin of the solar system exercised a profound 

 influence upon the fundamental conceptions of almost 

 every science during the entire nineteenth century. It 

 was the first successful effort in the modern doctrine of 

 evolution. 



The theory of the motion of the moon was a highly 

 favored subject during the first half of the last century. 

 The theory developed by Laplace was carried to a high 

 degree of perfection by DAMOISEAU (1768-1846). A 

 second theory was worked out extensively by DE PONTE- 

 COULANT (1795-1874); a third, and by far the most 

 perfect theory was developed by DELAUNAY (1816- 

 1872). The theory of Delaunay, which was the result 

 of twenty years of constant labor, was published between 

 1860 and 1867. 



A dramatic event about the middle of the nineteenth 

 century immortalized the names of LE VERRIER (1811- 

 1877) of France and ADAMS of England. Their mathe- 

 matical analysis led these two men independently to 

 point to a certain position in the sky and say, "In that 

 direction lies a planet not yet seen by mortal eyes." 

 This prediction, verified promptly by the telescope, has 

 been justly regarded as one of the great triumphs of 

 man's powers of analysis. It was also under Le Vender's 

 directions that the theory of the perturbations of the 

 planets was carried to its high state of perfection. 



In the last decade of the last century TISSERAND 

 (1845-) f Paris published his " Traite de la Mecanique 

 celeste," which is today the standard work of reference 

 in its field. It is complete in its details and embodies 

 all the essential developments in the field of celestial 

 mechanics up to the time of Poincare. 



