D'ALEMBERT. 469 



bear the application of the calculus. Then how was he 

 to be sure that any given branch of experimental philoso- 

 phy might not be susceptible of strictly mathematical 

 treatment, unless he made himself master of that branch"? 

 We find Cavendish applying geometrical and analytical 

 reasoning to such subjects as electricity. We have pro- 

 found Memoirs of my illustrious and lamented colleague, 

 M. Poisson, treating the same subject by the resources of 

 the calculus of which he was so great a master. Capil- 

 lary attraction received a similar consideration from 

 Laplace ; analysis has been successfully applied to 

 optical researches by mathematicians of our own times. 

 But I would not by any means be understood in these 

 observations to admit that purely inductive researches, 

 and those to which no geometrical reasoning can be 

 applied, are less worthy of a philosopher's regard than 

 those which easily ally themselves with the science of 

 necessary truth. No one who has studied the inimitable 

 experimental investigations of the second book of the 

 ' Optics/ can hesitate in admitting that they are in every 

 way worthy of the immortal author of the ' Principia.' 

 The inquiries of Black and Cavendish excite the like 

 admiration. Nay, has not D'Alembert himself written 

 many profound optical papers 1 We have some of these 

 in the 1st, 5th, and 7th volumes of the ' Opuscules/ and 

 the 3rd volume is composed wholly of such. How then 

 could he tell beforehand that he might not find other 

 physical subjects capable of geometrical treatment? 



It remains to note the inferiority in point of elegance 

 in D'Alembert's investigations to those of many other 

 geometricians. He was anxious only for the result ; and 

 the truth once discovered he was extremely indifferent to 



