CAILLE (NIcuosAs LEWIS DE LA,) in biography, an eminent French mathe matician and astronomer, was born in the diocese of Rheims in 1713. His father having quitted the army, in which he had served, amused himself in his retirement with studying mathematics and mecha nics, in which he proved the happy author of several inventions of considerable use to the public. From this example of his father, our author, almost in his in. fancy, took a fancy to mechaincs, which proved of signal service to him in his maturer years. At school he discov ered early tokens of genius. He next came to Paris in 1729, where he studi ed the classics, philosophy, and mathe matics. He afterwards studied divinity in the College de Navarre, with the view embracing the ecclesiastical life, hut never entered into priest's orders. His turn for astronomy soon connected him with the celebrated Cassini, who procured him an apartment in the observatory : where, assisted by the councils of this master, he soon acquired a name among the as tronomers. In 1739 lie was joined with M. Cassini de Thury, son to M. Cassini, in verifying the meridian through the whole extent of France ; and in the same year he was named professor of mathe matics in the College of Mazarine. In 1741 he was admitted into the Academy of Sciences, and had many excellent pa pers inserted in their memoirs ; besides which, he published several useful trea tises, viz. Elements of Geometry, Astro nomy, Mechanics, and Optics. He also carefuly computed all the eclipses of the sun and moon tnat had happened since the curistian zra, which were printed in the work, entitled " L'Art de verifier les Dates," &c. Paris, 1750, in 4to. He also compiled a volume of astronomical ephe merides for the years 1745 to 1755 ; an other for the years 1755 to 1765; and a third for the years 1765 to 1775; as also the most correct solar tables of any ; and an excellent work, entitled "Astronomic: Fundamenta novissimis Solis et Stellarum Observationibus stabilita." Having gone through a seven year's series of astronomical observations in his own observatory in the Mazarine College, he formed the project of going to observe the southern stars at the Cape of Good Hope ; being countenanced by the court, he set out upon this expedition in 1750, and in the space of two years he observed there the places of about 10,000 stars in the southern hemisphere, that are not vi sible in our latitudes, as well as many other important elements, viz. the paral
laxes of the sun, moon, and some of the planets, the obliquity jf the ecliptic, the refractions, &c. Having thus executed the purpose of his voyage, and no present opportunity offering for his return, he thought of employing the vacant time in another arduous attempt ; no less than that of taking the measure of the earth, as he had already done that of the heavens, he discovered, that the radii of the parallels in south latitude are not the same length as those of the corresponding parallels in north latitude. About the 23d degree of south latitude he found a degree on the meridian to contain 342222 Paris feet. The court of Versailles also sent him an order to go and fix the situa ation of the isles of France and of Bour bon.
M. de la Caille returned to France in the autumn of 1754, after an absence of about four years ; loaded, not indeed with the spoils of the East, but with those of the southern heavens, before then almost un known to astronomers. Upon his return, he first drew up a reply to some strictures which the celebrated Euler had published relative to the meridian; after which he settled the results of the comparison q his observations for the parallaxes, with those of other astronomers : that of the sun he fixed at 93"; of the moon at 56' 56"; of Mars in his opposition, 36"; of "Venus 38". He also settled the laws by which astronomical refractions are varied by the different density or rarity of the air, by heat or cold, and by dryness or moisture. And, lastly, he skewed an easy and practicable method of finding the longitude at sea by means of the moon. His fame being now celebrated every where, M. de la Caille was soon elected a member of most of the acade mies and Societies of Europe, as London, Bologna, Petersburgh,Berlin, Stockholm, and Gottingen. He died in 1762, aged 49.