.188 HISTORY OF PHYSICAL ASTRONOMY. 



space, time, and number; Newton's was a causal 

 law, referring these motions to mechanical reasons. 

 It is no doubt conceivable that future discoveries 

 may both extend and further explain Newton's doc- 

 trines; may make gravitation a case of some wider 

 law, and may disclose something of the mode in 

 which it operates; questions with which Newton 

 himself struggled. But, in the mean time, few per- 

 sons will dispute, that both in generality and pro- 

 fundity, both in width and depth, Newton's theory 

 is altogether without a rival or neighbour 24 . 



The requisite conditions of such a discovery in 

 the mind of its author were, in this as in other 

 cases, the idea, and its comparison with facts; 



24 The value and nature of this step have long been gene- 

 rally acknowledged wherever science is cultivated. Yet it would 

 appear that there is, in one part of Europe, a school of philoso- 

 phers who contest the merit of this part of Newton's discoveries. 

 "Kepler," says a celebrated German metaphysician*, le disco- 

 vered the laws of free motion ; a discovery of immortal glory. 

 It has since been the fashion to say that Newton first found out 

 the proof of these rules. It has seldom happened that the glory 

 of the first discoverer has been more unjustly transferred to 

 another person." It may appear strange that any one in the 

 present day should hold such language ; but if we examine the 

 reasons which this author gives, they will be found, I think, to 

 amount to this; that his mind is in the condition in which 

 Kepler's was ; and that the whole range of mechanical ideas and 

 modes of conception which made the transition from Kepler to 

 Newton possible, are extraneous to the domain of his philosophy. 

 Even this author, however, if I understand him rightly, recog- 

 nizes Newton as the author of the doctrine of Perturbations. 

 * Hegel, Encyclopedia, 270., 



