Joseph Jerome Le Francais De Lalande, a French astronomer, born in Bourg-en-Bresse, July 11, 1732, died in Paris, April 4, 1807. His family name was Le Francais, but he assumed that of Lalande at the outset of his scientific career. He was educated in the college of the Jesuits at Lyons, and was sent to Paris to study law; but making the acquaintance of De Lisle, he devoted himself to astronomy under him and Le Monnier. The latter in 1751 procured him a scientific mission to Berlin, where he was to ascertain, through astronomical observations, the distance between the earth and the moon, while La Caille was making similar observations at the Cape of Good Hope. He was presented to Frederick the Great, and, although but 19 years old, was made a member of the Berlin academy of sciences. On his return in 1753, he was elected to the French academy of sciences, assisted Clairaut in his researches on comets, especially that of Halley, and in 1760 became the editor of the Connaissance des Temps, which he conducted till 1775, and subsequently from 1794 till his death. In 1762 he succeeded De Lisle in the chair of astronomy at the college de France, and during 45 years delivered lectures on that science.

He reached the height of his fame when he published a map illustrating the two transits of Venus which were to take place in 1761 and 1769, and showing the exact time of those transits for all countries on the globe. About the same time he announced to the world the results of the calculations through which the distance between the sun and the earth had been definitely ascertained. He gave much attention to navigation, and delivered lectures and published works on this subject, which are highly valued. But the popularity acquired by his scientific labors did not satisfy his thirst for fame; and in order to keep public curiosity constantly alive, he stationed himself on the Pont-Neuf to give astronomical explanations to passers by; announced that he would travel in a balloon from Paris to Gotha, where a scientific congress was to be held; had it reported that he ate spiders, caterpillars, worms, and other insects; and professed the boldest atheism. Lalande's principal work is the Traite d'istronomie (2 vols. 4to, Paris, 1764), which exceeded in utility all previous treatises of the kind.