D'ALEMBERT. 389 



after he had held the highest offices and been engaged 

 in the most dissimilar discussions. As late as 1838, 

 when I was engaged in preparing my Analytical Re- 

 view of the Principia, I found that, by an accidental 

 coincidence, he was amusing his leisure with the cal- 

 culus long intermitted ; and I am sure that he could 

 have furnished as correct and more elegant analytical 

 demonstrations of the Newtonian theorems than 1 had 

 the fortune to obtain in composing that work. 



I have thought it a useful thing to consider the 

 personal history with the scientific achievements of a 

 very great geometrician, with a view to the illustration 

 of these remarks and I have chosen D'Alembert in 

 preference to Euler or to Clairaut, the two other illus- 

 trious analysts of their age, because we have more 

 ample materials for the study. Whatever of peace 

 and comfort he enjoyed, D'Alembert owed to geometry, 

 and confessed his obligations. Whatever he suffered 

 from vexation of any sort, he could fairly charge upon 

 the temporary interruption of his mathematical pur- 

 suits. In both portions of his history, therefore, it is 

 likely to prove instructive, and to enforce the doctrine 

 which I have laid down. 



Jean le Rond d'Alembert was born on the 17th of 

 Nov., 1717, being a foundling exposed near the church 

 of St. Jean le Rond in Paris, and thus called by the 

 name of the parish, as is usual in most countries. The 

 commissary of the district, before whom the infant was 

 carried, perceiving its feeble and almost dying condi- 

 tion, instead of sending it to the hospital gave the 

 charge to the wife of a poor but honest glazier in the 

 neighbourhood, living in the Rue Michel-le-Comte, for 

 he was acquainted with the good woman's respecta- 

 bility. In a few days the father, M. Destouches, 

 commissary of artillery, came forward to own the 

 child, and made provision for its support. The general 

 belief is, that the exposition had been concerted with 

 the police. But if so, a very needless risk was unac- 



