D'ALEMBERT. 421 



were great men of congenial habits. He had now 

 passed his thirty-fifth year 



" II mezzo di camin di nostra vita." Dante. 



His devotion to the mathematics had all along 

 estranged him from those branches of physical science 

 which do not lend themselves to analytical investiga- 

 tion. Indeed, as I have shown in the Life of Simson, 

 he appears even to have disregarded all geometrical in- 

 quiries which were unconnected with modern analysis. 

 But he had always cultivated a taste for the belles- 

 lettres, and both read and understood poetry. He was 

 also well acquainted with moral and metaphysical sub- 

 jects. The singularity is, therefore, great, that he should 

 have had no taste for the inductive sciences. Herein 

 he differed widely from other great geometricians. To 

 say nothing of the greatest of mathematicians, Newton 

 himself, alike of inexhaustible resources in experimental 

 as in analytical and geometrical investigation, Euler and 

 Laplace both were much attached to experimental 

 philosophy. D'Alembert had, moreover, lived in the 

 society of several persons whose pursuits were not at 

 all confined to the mathematics, and with some for 

 whom that science had no attractions. Of these Diderot 

 was his most intimate and earliest friend; and he it 

 was who prevailed upon him to join in the conduct of 

 a great literary undertaking, the first French Encyclo- 

 psedia. This w^ork was published at Paris from 1751 

 to 1758 ; and of these seven volumes D'Alembert and 

 Diderot were the joint editors. D'Alembert also con- 

 tributed many of the best articles, and wrote the cele- 

 brated Preliminary Discourse upon the distribution and 

 the progress of the sciences. The merit of those arti- 

 cles is generally, as might have been expected from 

 such a writer, great in proportion as he exerted him- 

 self to elaborate and to finish them. But the best are, 

 as might also have been expected, the mathematical. 



The Preliminary Discourse has, in my very humble 



