46 KEPLER of banishment against Protestant preachers and professors. Kepler immediately fled to the Hungarian frontier, but, by the favour of the Jesuits, was recalled and reinstated in his post. The gymnasium, however, was deserted; the nobles of Styria began to murmur at subsidizing a teacher without pupils ; and he found it prudent to look elsewhere for employment. He first turned to his native country ; but his refusal to subscribe unconditionally to the rigid formula of belief adopted by the theologians of Tubingen permanently closed against him the gates of his alma mater. His embarrassment was relieved by a letter from Tycho Brahe offering him the position of assistant in his obser vatory near Prague, which, after a preliminary visit of four months, he accepted. The arrangement was made just in time; for on August 7, 1600, he received definitive notice to leave Gratz, and, having leased his wife s property, departed with his family for Prague, September 30. His relations with Tycho were not of an entirely agreeable character. The Danish astronomer, though benevolent, was haughty and overbearing ; Kepler s natural irritability was aggravated by prolonged fever, by pecuniary anxieties, and by domestic mismanagement. Nevertheless, after one violent quarrel, smoothed over by mutual concessions, they maintained an amicable intercourse, unexpectedly termi nated by Tycho s death, October 24, 1601. A brilliant and prosperous career seemed by this event to be thrown open to Kepler. The emperor Rudolph IL immediately appointed him to succeed his patron as imperial mathematician, although at a reduced salary of 500 florins ; the invaluable treasure of Tycho s observations was, after some futile opposition on the part of his heirs, placed at his disposal ; and the laborious but congenial task was entrusted to him of completing the tables to which the grateful Dane had already affixed the title of RudolpMne. The first works executed by him at Prague were, however, a homage to the astrological proclivities of the emperor. In De fundamentis astrologise certioribus (Prague, 1602) he declared his purpose of preserving and purifying the grain of truth which he believed the science to contain. Indeed, the doctrine of "aspects" and "influences" fitted excellently with his mystical concep tion of the universe, and enabled him to discharge with a semblance of sincerity the most lucrative part of his pro fessional duties. Although he strictly limited his prophetic pretensions to the estimate of tendencies and probabilities, his forecasts were none the less in demand. Shrewd sense and considerable knowledge of the world came to the aid of stellar lore in the preparation of " prognostics " which, not unfrequently hitting off the event, earned him as much credit with the vulgar as his cosmical speculations with the learned. He drew the horoscopes of the emperor and Wallenstein, as well as of a host of lesser magnates ; but, though keenly alive to the unworthy character of such a trade, he made necessity his excuse for a compromise with superstition. " Nature," he wrote, " which has conferred upon every animal the means of subsistence, has given astrology as an adjunct and ally to astronomy." He dedicated to the emperor in 1603 a treatise on the " great conjunction " of that year (Judidum de trigono igneo] ; and he published his observations on a brilliant star which appeared suddenly, September 30, 1604, and; remained visible for seventeen months, in De stella nova in pede Serpentarii (Prague, 1606). While sharing the opinion of Tycho as to the origin of such bodies by condensation of nebulous matter from the Milky Way, he attached a mystical signification to the coincidence in time and place of the sidereal apparition with a triple conjunction of Mars, Jupiter, and Saturn. The main task of his life was not meanwhile neglected. This was nothing less than the foundation of a new astronomy, in which physical cause should replace arbitrary hypothesis. A preliminary study of optics led to the publication, in 1604, of his Astronomiee pars optica, con taining important discoveries in the theory of vision, and a notable approximation towards the true law of refraction. But it was not until 1609 that, the "great Martian labour" being at length completed, he was able, in his own figura tive language, to lead the captive planet to the foot of the imperial throne. From the time of his first introduction to Tycho he had devoted himself to the investigation of the orbit of Mars, which, on account of its relatively large eccentricity, had always been especially recalcitrant to theory, and the results appeared in Astronomia nova curioAoy^Tos, seu Physica coelestis tradita commentariis de motibus stellae, Marlis (Prague, 1609). In this, the most memorable of Kepler s multifarious writings, two of the cardinal principles of modern astronomy the laws of elliptical orbits and of equal areas were established ; x important truths relating to gravity were enunciated, and the tides ascribed to the influence of lunar attraction ; while an attempt to explain the planetary revolutions in the then backward condition of mechanical knowledge pro duced a theory of vortices closely resembling that after wards adopted by Descartes. Having been provided, in August 1610, by Ernest, archbishop of Cologne, with one of the new Galilean instruments, Kepler began, with unspeakable delight, to observe the wonders revealed by it. He had welcomed with a little essay called Dissertatio cum Nuncio Sidereo Galileo s first announcement of celestial novelties ; he now, in his Dioptrice (Augsburg, 1611), expounded the theory of refraction by lenses, and suggested the principle of the " astronomical " or inverting telescope. Indeed the work may be said to have founded the branch of science to which it gave its name. The year 1611 was marked by Kepler as the most disastrous of his life. The death by small-pox of his favourite child was followed by that of his wife, who, long a prey to melancholy, was at last, July 3, carried off by typhus. In his review of their conjugal life, remorse for frequent outbursts of impatience towards his shiftless though well-meaning helpmate took the place of regret for her loss. Public calamity was added to private bereave ment. On the 23d of May 1611 Matthias, brother of the emperor, assumed the Bohemian crown in Prague, compel ling Rudolph to take refuge in the citadel, where he died on the 20th of January following. Kepler s fidelity in remaining with him to the last did not deprive him of the favour of his successor. Payment of arrears, now amount ing to upwards of 4000 florins, was not, however, in the desperate condition of the imperial finances, to be hoped for ; and he was glad, while retaining his position as court astronomer, to accept (in 1612) the office of mathematician to the states of Upper Austria. His residence at Linz was troubled by the harsh conduct of the pastor Hitzler, iii excluding him from the rites of his church on the ground of supposed Calvinistic leanings a decision con firmed, with the addition of an insulting reprimand, on his appeal to Wiirtemberg. In 1613 he appeared with the emperor Matthias before the diet of Ratisbon as the advo cate of the introduction into Germany of the Gregorian calendar ; but the attempt was for the time frustrated by anti-papal prejudice. The attention devoted by him to chronological subjects is evidenced by the publication about this period of several essays in which he sought to prove that the birth of Christ took place five years earlier than the commonly accepted date. Kepler s second courtship forms the subject of a highly characteristic letter addressed by him to Baron Stralendorf, See ASTRONOMY, vol. ii. p. 752.
