Monnier, Peter Charles Le

, an eminent French astronomer and mathematician, was born at Paris, Nov. 23, 1715. His education was chiefly directed to the sciences, to which he manifested an early attachment; and his progress was such that at the age of twenty-one, he was chosen as the co-operator of Maupertuis, in the measure of a degree of the meridian at the polar circle. At the period when the errors in Flamsteed’s catalogue of the stars began to be manifest, he undertook to determine anew the positions of the zodiacal stars as being the most useful to | astronomers. In 1743 he traced at St. Sulpice a grand meridian line, in order to ascertain certain solar motions, and also the small variations in the obliquity of the ecliptic.

In 1746, he determined, after numerous observations, the great inequalities of Saturn, produced by the action of Jupiter; and his work served as a foundation for the paper of Euler on this subject, which gained the prize at the academy of sciences in 1748. Soon after this, Le Monnier published his “Astronomical Institutions,” a work which was so much the more useful, as it was then the only one in France that contained the first principles of astronomy. Having undertaken to determine the errors of the lunar tables, he directed his labours peculiarly to that satellite, which he observed with assiduity during the entire period of eighteen years, at the end of which the same errors should recommence. His principal works, besides the foregoing, are “Lunar Nautical Astronomy,” “Tables of the Sun,” and “Corrections of those of the Moon.” He took great pleasure in astronomical observations, and to him has been ascribed the great improvement that has taken place in France in practical astronomy.

During his long career he was considered among his friends as the soul of astronomy, and made numerous proselytes to this study by his advice, example, and instructions. It is to him we chiefly owe the early progress of two celebrated astronomers, Lalande and Pingre. Le Monnier died in 1799, in the 84th year of his age. He had a brother, Lewis William, a very able experimental philosopher, but who is not to be confounded with an abbe of that name who translated Terence and Persius into French, and who was the author of fables, tales, and epistles. The latter died in 1796. ¹