JOHN, one of the most eminent astronomers who have appeared in any age, was born at Wiel on the 27th of December 1571. His father's name was Henry Kepler, an officer of distinction among the troops of Wittenberg, but reduced to poverty by numerous misfortunes. This exposed young Kepler to many difficulties and interruptions while acquiring the rudiments of his education; but such was his genius, and such his avidity for knowledge, that he surmounted every difficulty, and his proficiency was astonishing. He studied at the university of Tubingen, where he obtained the degree of bachelor in the year 1588, and that of master of philosophy in 1591. In the year 1592 he applied himself to the study of divinity; and the sermons he produced were sufficient indications that he would have excelled as a preacher, had he continued in the clerical profession. The mathematics, however, became his favourite study, for his knowledge of which he acquired such distinguished reputation, that he was invited to Gratz in Styria in the year 1594, to fill the mathematical chair in the university of that city. After this period his chief attention was directed to the study of astronomy, and he made many interesting discoveries respecting the laws of planetary motions.

Two years after his marriage with a lady descended from a noble family, persecution on account of his religion compelled him to quit Gratz, to which he was afterwards recalled by the states of Styria. The calamities of war, however, induced him to look for a residence where he might enjoy greater safety and tranquillity. During this uncomfortable situation of affairs, the celebrated Tycho Brahe strongly urged him to settle in Bohemia as his assistant, where he himself had every necessary requisite furnished to him by the emperor Rudolph, for the prosecution of his astronomical studies. The numerous and urgent letters which Kepler received upon this subject, and solemn assurances that he should be introduced to the emperor, at length prevailed with him to leave the university, and settle in Bohemia with his family in the year 1600. On his way to that country he was seized with a quartan ague, which afflicted him for seven or eight months, and rendered him incapable of contributing that aid to Tycho which he would otherwise have done. He was likewise displeased with the conduct of this astronomer towards him, and thought that he behaved in an unfriendly manner, by neglecting to do a material service to his family when he had it in his power. Kepler also considered him as by far too reserved, in not communicating to him the whole of his discoveries and improvements.

The death of Tycho happened in 1601; and thus the intercourse between these two eminent men being of such short duration, precluded Kepler either from being very serviceable to, or deriving much advantage from, the investigations and researches of the Danish astronomer. Kepler, however, was introduced to the emperor by Tycho, in conformity to his promise, and appointed mathematician to his imperial majesty, with instructions to complete the Rodolphine Tables which that great man had begun. These were not published till the year 1627, owing to a variety of obstructions and difficulties which were thrown in his way. Two years after the publication of this work, he went to Ratibon, by permission of the emperor, to claim payment of the arrears of his pension, where he was seized with a violent fever, supposed to have been brought upon him by too hard riding; and to this he fell a victim in the month of November 1630, in the 59th year of his age.

The learned world is indebted to this sagacious and able astronomer and mathematician for the discovery of the true figure of the planetary orbits, and the proportions of the motions of the solar system. Like the disciples of Pythagoras and Plato, Kepler was seized with a peculiar passion for finding analogies and harmonies in nature; and although this led him to the adoption of very strange and ridiculous conceits, we shall readily be disposed to overlook these, when we reflect that they were the means of leading him to the most interesting discoveries. He was for some time so charmed with the whimsical notions contained in his Mysterium Cosmographicum, published in 1596, that he declared he would not give up the honour of having invented what was contained in that book for the electorate of Saxony;—so easy is it for the greatest of men to be deceived by a dazzling hypothesis.

He was the first who discovered that astronomers had been invariably mistaken in always ascribing circular orbits and uniform motions to the planets, since each of them moves in an ellipse, having one of its foci in the sun; and, after a variety of fruitless efforts, he, on the 15th of May 1618, made his splendid discovery "that the squares of the periodic times of the planets were always..."