378 



SCIENTIFIC THOUGHT. 



42. 

 Is the New- 



mula an 

 ultimate 

 law? 



43. 



Laplace's 

 opinion. 



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- 

 sophical question, the further and more modest ques- 

 tion can be raised, Does 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: 1 "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 

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

 in perfecting the astronomical theories founded upon the 



1 ' Exposition du Systeme du 

 Monde,' 6th ed., p. 318. 



2 Tisserand, in discussing the diffi- 

 culties which still beset the lunar 

 theory, and after referring to the 

 " prix Damoiseau " offered by the 

 Academy of Sciences for an essay 

 on this subject, says ('Bulletin 

 astronomique,' 1891, vol. viii. p. 

 501): "La the"orie de la lune se 



trouve arrete"e par la difficult^ que 

 nous venons de developper ; dej'a 

 a l'e"poque de Clairaut la gravita- 

 tion universelle paraissait impuis- 

 sante a expliquer le mouvement 

 du pe'rige'e ; elle triomphera encore 

 du nouvel obstacle qui se pre'sente 

 aujourd'hui, mais il reste a faire une 

 belle de"couverte. " 



