ALEMBERT (Jogs LE ROND D') an eminent French mathematician and philo sopher, and one of the brightest orna ments of the 18th century. He was per petual secretary to the French Academy of Sciences and a member of most of the philosophical academies and societies of Europe.
D'Alembert was born at Paris, the 16th of November, 1717, and derived the name of John le Rond, from that of the church, near which, after his birth, he was exposed as a foundling. But his fa ther, Destouches Canon, informed of this circumstance, listening to the voice of nature and duty, took measures for the proper education of his child, and for his future subSistence in a state of ease and independence. His mother, it is said, was a lady of rank, the celebrated Ma demoiselle Tencin, sister to cardinal Ten cin, archbishop of Lvons.
Ile received his first education among the Jansenists, in the College eff the Four :cations, where he gave early signs of genins and ciipacity. ln the first year of his philosophical studies, he composed a Commentary on the Epistle of St. Paul to the Romans. The Jansenists considered this production as an omen, that portend ed to the party of Port-Royal a restora tion to some part of their former splen dour,and hoped to find one day,in D'Alem bert, a second Pascal. To render the resemblance more complete, they enga ged their pupil in the study- of the ma thematies; but they soon perceived that his growing attachritent to this science was likely to disappoint the hopes they had formed with respect to his future des tination ; they therefore endeavoured to divert lihn from the pursuit; but their endeavours were fruitless: On his quitting the college, finding himself alone, apd unconnected in the world, he sought an asylum in the house of his nurse, who was the wife of a gla zier. He hoped that his fortune, though not ample, would enlarge the subs;stence, and better the condition of her family, which was the only one tha.t he couid consider as his own. It was here, there. fore, that he fixed hisresidenceoresolving to apply himself entirely to the study of geometry. And here he lived, during the space of 30 years, with the greatest sim plicity, discovering the augmentation of his means only by increasing displays of his beneficence, concealing his growing reputation and celebrity from these ho nest people, and making their plain and uncouth manners the subject of good natured plea.santry and philosophical ob
servation. His good nurse perceived his ardent activity ; heard him mentioned as the writer of many books; and beheld him with a kind of compassion : "You will never," said. she to him one day, "be any thing but a philosopher--and what is a philosopher ?—a fool, who toils and plagues himself all his life, that peo ple inay talk of him when he is dead." As D'Alembert's fortune did not far exceed the demands of necessity, his friends advised him to think of some pro cession that might enable him to increase it. He accordingly turned his views to the law, and took his degrees in that fa culty, which he soon after abandtmed, • and applied himself to the study Of me dicine. Geometry, however, was always drawing him back to his former pursuits : SO that, after army ineffectual struggles to resist its attractions, he renounced all views.of a lucrative profession, and gave himself up entirely to mathematics and poverty. In the year 1741 he was ad mitted &member of the Academy of Sci. ences ; for which distinguished literary, promotion, at so early an age (24,) lie had prepared the way, by correcting the errors of the "Analyse Demontree" of Reyneau, which was highly esteemed in France in the line of analy-ties. Ile after wards set himself to examine, with atten tion and assiduity, v.-hat must be the mo t4on and path of a body, which passes from one fluid into anotker denser _ _ in a direction oblique to the surrace be tween tile two fl aids. Two y ears after his election to a place in the academy, he published his "'Treatise on Dynamics." The new princinle developea it, this treatise consiSteclin establishing an etym.. lity, at each instant, between the changes that the motion of a body has iindergone, and the forces or powers which have been employed to prodiice them ; or, to ex press the same thing otherwise, in sepa rating into two parts the action of the moving pnwers. and considering the one :19 producing alone the motion of the bo dy in the second instant, and the other a.s employed to destroy that wWch it had in the first.