Kepler

JOHANN, (kep'lur,) one of the greatest of modern astronomers, B. at Weil, in Würtemberg, 1571. On the death of Tycho Brahe, 1601, K. succeeded him as principal mathematician to the emperor Rudolph; but the treasury of the emperor was so much exhausted by war that K. could not obtain the payment of his salary, and often felt the pre ure of poverty. In 1612, he was appointed profe or of mathematics at Linz, and D. at Ratisbon, 1630. He expended the labor of several years on his " Rudolphine Tables," which were published in 1627, and have been highly prized. He also made great discoveries in optics, general physics, and geometry. But his chiefest title to lasting fame is his Astronomia Nova, which was produced in 1609, and in which he announced the laws which govern the planetary motions. These laws, known as Kepler's Laws, are three in number:-1. The planets describe ellipses, each of which has one of its foci in the sun. 2. Every planet moves, so that the line drawn from it to the sun describes about the sun areas proportional to the times. 3. The squares of the times of the revolutions of the planets are as the cubes of their mean distances from the sun. [s. 515]