GRANGE, JosENT-Lours L.t,* a celebrated mathema tician and natural philosopher, was born at Turin, on the 25th of November, 1736. He was the son of Joseph Lou is la Grange, treasurer of war, and of Marie-Therese Gros, only daughter of a rich physician of Cambiano.
His father was rich, and had made an advantageous marriage : but was ruined by hazardous undertakings. Let us not, however, lament the situation of M. la Grange. He himself viewed it as the first cause of all the good for tune that afterwards hefel him. " Had I been in posses sion of a fortune," said he, " I should not probably have studied mathematics." In what other situation would he have found advantages that could enter into comparison with those of a tranquil and studious life, with that splen did series of discoveries in a branch of science considered as the most difficult, and with that personal respectability which was continually increasing to the very last period of his life ? His taste for mathematics did not appear at first. He was passionately devoted to Cicero and Virgil, before he could read Archimedes and Newton. He then became au enthusiastic admirer of the geometry of the ancients, which he preferred to the modern analysis. A memoir which the celebrated Halley had composed long before, to demon strate the superiority of the analytic method, had the glo ry of converting him, and of teaching him his true destiny. He devoted himself to this new study with the same suc cess that he had in the synthesis, and which was so deci ded, that at the age of 16 he was professor of mathematics in the Royal Military School. The extreme youth of a professor is a great advantage to him when he has shown extraordinary abilities, and when his pupils are no longer children. All the pupils of M. la Grange were older than himself, and were not the less attentive to his lectures on that account. He distinguished some of them, whom he made his friends.
From this association sprung the academy of Turin, which in 1759 published a first volume, entitled Acts of a private Society. We see there the young La Grange di
recting the philosophical researches of the physician Cig na, and the labours of the Chevalier de Saluces. He fur nished to Foncenex the analytical part of his memoirs, leaving to him the task of developing the reasoning upon which the formula depended. In these memoirs, which do not bear his name, we observe that purely analytical method, which afterwards characterised his great produc tions. He had discovered a new theory of the lever. It constitutes the third part of a memoir, which was very suc cessful. Foncenex, in recompense, was placed at the head of the Marine, which the king of Sardinia formed at that time. The two first parts have the same style, and seem written by the same person. Do they likewise be long to La Grange ? He never expressly laid claim to them ; but what may throw some light on the real author is, that Foncenex soon ceased to enrich the volumes of the new academy, and that Montucla, ignorant of what La Grange revealed to us during the latter part of his life, is astonished that Foncenex interrupted those researches which might have given him a great reputation.
M. la Grange, while he abandoned to his friend insula ted theorems, published at the same time, under his own name, theories which he promised to develope further. Thus after having given new formula of the maxinzum and minimum in all cases, after having shown the insufficiency of the known methods, he announces that he will treat this subject, which lie considered as important, in a work which he was preparing, in which, would be deduced from the same principles all the mechanical properties of bodies, whether solid or fluid. Thus at the age of 23 he had laid the foundation of the great works, which have commanded the admiration of philosophers.
In the same volume he reduces under the differential calculus the theory of recurrent series and the doctrine of chances ; which before that time had only been treated by indirect methods. He established them upon more natural and general principles.