CLAIRAUT, or CLAIRAUT, ALEXIS-CLAUDE, was born
May 7, 1713, at Paris, where his father was a teacher of ma-
thematics. Under his father's tuition he made so rapid pro-
gress in mathematical studies, that in his thirteenth year he
read before the French Academy a memoir of the properties
of four curves which he had then discovered. When only
sixteen, he finished his treatise on Curves of Double Curvature,
which, at its publication, two years later, procured his
admission into the Academy of Sciences, although even then
he was below the legal age. Having formed an acquaint-
ance with Maupertuis, Lemonnier, and others, he began his
researches on the figure of the earth, the results of which
were published in 1743. In his work on this subject he
promulgated his famous theorem in regard to the variation
of gravity, which has been corrected by Mr Airy. In 1750
he gained the prize of the St Petersburg Academy, for his
treatise on the Lunar Theory; and in 1759 calculated the
perihelion of Halley's Comet. Towards the close of his life
he was regarded as the great rival of D'Alembert. Clairaut
died at Paris, May 17, 1765. See ASTRONOMY.