EWLER, LEONARD, one of the greatest of mathematicians, was b. at Basel, April 15, 1707, and received his first instructions in the science, for which he afterwards did so much, from his father, who was pastor of the neighboring village of Riechen. At the university of Basel, he studied under John Bernouilli, and was the friend of Daniel and Nicholas Bernouilli. At the age of 19, he was second in the contest for a prize offered by the academy of Paris for the best treatise on the masting of ships. His friends, the Bernouillis, had been called to St. Petersburg by Catharine I., when she founded the academy, and they now induced E. to settle in that capital, in 1730, as professor of physics. Three years later he exchanged his professorship for a place in the academy. From that time he continued to labor in the field of mathematics with an ardor really astonishing. More than half the mathematical treatises in the 46 quarto volumes published by the St. Petersburg academy from 1727-83 are by E., and at his death he left more than 200 treatises in MS., which were afterwards published by the academy. The Paris academy of science awarded him the prize on ten several occa sions, one of which was his treatise on Tides, 1740. In 1741, he accepted the invitation of Frederick the great to Berlin. He afterwards, 1760, returned ,ts St. Petersburg, where he was made director of the mathematical department of the academy, and died Sept. 7, 1783. The last years of his life were spent in total blindness.
E. was of an amiable and religious character, always cheerful and good-humored; in society, he was distinguished for his agreeable wit. It was doubtless his residence in St. Petersburg that led him to the application of mathematics to the building and management of ships, as embodied in his Theorie de la Construction et de la .Manoeuvre des Vaisseaux (Petersb. 1773). The great problems left by Newton to his successors were the objects of his unceasing research. On physical subjects, E. often adopted extremely untenable hypotheses. He occupied himself also with philosophy in the proper sense of the word. He undertook to prove the immateriality of the soul, and to defend revelation against freethinkers. In his Lettres a tine Princesse d' Allentagne stir quelques &jets de Physique et de Philosophie (3 vols., Berl. 1768; new ed., Par. 1812; and which have also been translated into English), he attacked Leibnitz's system of monads and of a pre-established harmony. But this was not the field in which he was Lest calculated to shine; his proper domain was the abstruser parts of pure mathematics. His most important works of this class are his Theory of Planetary Motion; Introduction. to the Analysis of Infinites; Institutions of the Threrential and of the Integral Calculus; and Dioptrics; which are all, as well as his Opuscula Analytica, in Latin. His Introduction. to Algebra is well known.