KEPLER, Johann, German astronomer and mathematician: b. Weil der Stadt. Wfirtem berg. 27 Dec. 1571; d. Regensburg (Ratisbon), 15 Nov. 1630. A contemporary of Galileo and Tycho Brahe, Kepler was one of the world's greatest astronomers, the real founder of mod ern astronomy; the one who first reduced the theory of the telescope to its true principles and laid down the common rules for finding the focal lengths of single lenses, and the magnify ing power of telescopes. His excursions in geometry produced epoch-making results; he established the symbolism of the sectio divina or pro portio divina, now known as the "golden sec tion,) and towered above all his contemporaries in stereometric investigation. Prematurely born of youthful, ill-matched parents, Kepler was physically a weakling, neglected in childhood and spending his early student years between strug gling for an education and working in his father's tavern. He worked his way through elementary schools by winning scholarships which enabled him to reach the University of Tiibingen. In 1593 he was appointed a teacher of mathematics at Gratz (Styria), where he de voted himself with much ardor to the study of astronomy, and attracted the attention of Tycho Brahe (n.v.) by dissertations on celestial orbits. But in 1599 religious persecutions commenced in Styria, and Kepler, being a Protestant, gladly accepted Tycho Brahe's invitation to Prague, to assist in the preparation of the new astro nomical tables, called the Rodolphine tables. Tycho died in 1601 and Kepler continued the work alone, being appointed imperial mathe matician and astronomer. After many years of incessant labor the tables were completed in 1624 and published in 1627 at Ulm. Kepler had
become the possessor of all Tycho Brahe's papers and the mass of observations made by that astronomer during 20 years, with a precision till then unsurpassed, enabled Kepler to establish the famous 'Kepler's Laws' (q.v.), which have proved so fruitful in the develop meat of astronomical science. Kepler enjoyed the patronage of the Emperors Rodolph and Ferdinand, the dukes of Wiirtemberg and Wal lenstein, but his life was a continued struggle with poverty; his salary was frequently in arrears and he was exposed to much religious persecution, while his domestic relations were equally unfortunate. The latter part of his life was chiefly passed at Linz as professor of mathematics. He wrote much, but the work that has rendered him immortal is his 'Astro nomia Nova, seu Physica Ccelestis tradita Com mentaries de Motibus Stella: Martis' New As tronomy, or Celestial Physics delivered in Com mentaries on the Motions of Mars) (1609). His MundP appeared in 1619; and among other works may be cited 'De Stella Nova in Pcde SerpentariP (1606) ; 'De Come (1619-20) ; 'Chinas Logarithmorum) (1624). Consult 'Lives' by Brewster Gunther and Muller; also Breitschwert, Vann Keplers Leben und Wirken' (1831) asner, 'Tycho Brahe und Kepler in Paw) (1872) ;• Reitlinger, 'Johann (1868); Reuschle, 'Kepler und die Astronomic> (1871). An excellent biography of Kepler is given in 'Allgemeine Deutsche Biographie' (Vol. XV, Leipzig 1882); Bryant, W. W., 'History of Astronomy' (Lon don 1907).