D'ALEMBEKT. 451 



proval to the whole of human conduct, which of neces- 

 sity proceeds upon the admission that contingent truths, 

 both physical and moral, rest on sufficient grounds for 

 us safely to act upon them in all the affairs of life ? 

 Besides, D'Alembert admitted, both in theory and by 

 his own conduct, that physical science was deserving 

 of attention, when it could bear the application of the 

 calculus. Then how could he be sure that any given 

 branch of experimental philosophy might not be sus- 

 ceptible of strictly mathematical treatment, unless he 

 made himself master of that branch? We find Caven- 

 dish applying geometrical and analytical reasoning to 

 such subjects as electricity. We have profound Me- 

 moirs 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 op- 

 tical 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 ? 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 ; 



