378 SCIENTIFIC THOUGHT. 



capable of finding out the ultimate properties of things, 



is a question which has been answered in opposite 



. ways. But whatever the answer may be to this philo- 



Is the New- 



muif^ or sophical question, the further and more modest ques- 

 uitimate ft on can ^ ^^g^ j) oes the gravitation formula express 

 one of those universal facts which we have to accept 

 as final, beyond or behind which we cannot penetrate ? 

 Opposite answers have been given to this question. But 

 it stands very much in the same position in which 

 Laplace left it when he said : l " The extreme difficulty 

 of the problem referring to the system of the universe 

 obliges us to have recourse to approximations, which 

 leave room for the fear that the neglected quantities 

 may have a sensible influence on the results. As soon 

 as mathematicians by observation became aware of this 

 influence they returned to their analysis : by rectifying 

 the same they have always found the cause of the ob- 

 served anomalies ; they have determined the laws of 

 these, and frequently they have outrun observation by 

 discovering irregularities which had not yet been ob- 

 served. The lunar theory, the theory of Saturn, of 

 Jupiter and his satellites, offer many examples of this 

 43. kind. 2 Thus we may say that nature herself has helped 

 opinion. 3 in perfecting the astronomical theories founded upon the 



1 Exposition du Systeme du J trouve arretee par la difficult* que 



Monde,' 6th ed., p. 318. nous venons de developper; deja 



'-' Tisserand, in discussing the diffi- a 1'epoque de Clairaut la gravita- 



culties which still beset the lunar tion universelle paraissait impuis- 



theory, and after referring to the sante a expliquer le mouvement 



"pfix Damoiseau " offered by the du peVigee; elle triomphera encore 



Academy of Sciences for an essay ! du nouvel obstacle qui se presente 



on this subject, says ('Bulletin ! aujourd'hui, mais il reste a faire une 



astronomique,' 1891, vol. viiL p. , belle decouverte." 



501): "La theorie de la lune se i 



