98 HISTORY OF MECHANICS. 



actual motions must be. The difficulty of deter- 

 mining the laws of equilibrium, in the application 

 of this principle in complex cases, is, however, often 

 as great as if we apply more simple and direct con- 

 siderations. 



5. Motion in Resisting Media. Ballistics. 

 We shall notice more particularly the history of 

 some of the problems of mechanics. Though 

 John Bernoulli always spoke with admiration of 

 Newton's Principia, and of its author, he appears 

 to have been well disposed to point out real or 

 imagined blemishes in the work. Against the 

 validity of Newton's determination of the path de- 

 scribed by a body projected in any part of the 

 solar system, Bernoulli urges a cavil which it is 

 difficult to conceive that a mathematician, such as 

 he was, could seriously believe to be well founded. 

 On Newton's determination of the path of a body 

 in a resisting medium, his criticism is more just. 

 He pointed out a material errour in this solution : 

 this correction came to Newton's knowledge in 

 London, in October 1712, when the impression of 

 the second edition of the Principia was just draw- 

 ing to a close, under the care of Cotes at Cam- 

 bridge : and Newton immediately cancelled the leaf 

 and corrected the errour 1 . 



This problem of the motion of the body in a 

 resisting medium, led to another collision between 

 the English and the German mathematicians. The 

 1 MS. Correspondence in Trin. Coll. Library. 



