KEPLER, 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 in the army of Wirtemberg, but reduced to poverty by numerous misfortunes. This exposed young Kepler to many difficulties and interruptions whilst acquiring the rudiments of his education; but such was his genius and his avidity for knowledge, that he surmounted every difficulty, and made astonishing proficiency. 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 afforded sufficient indication that he would have excelled as a preacher had he continued in the clerical profession. The mathematics, however, became his favourite study; and he soon acquired such distinguished reputation as a geometrician, 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 the 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 out 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 Rodolph for the prosecution of his astronomical studies. The numerous and urgent letters which Kepler received upon this subject, and the solemn assurances that he should be introduced to the emperor, at length induced him to leave the university, and settle in Bohemia with his family, in the year 1600. But 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 further, considered him as by far too reserved, in not communicating to him the whole of his discoveries and improvements. Tycho died in the year 1601, and the intercourse between these two eminent men being thus of short duration, precluded Kepler from being either 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 commenced. 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, by permission of the emperor, to Ratisbon, to claim payment of the arrears of his pension, but he was there 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 fifty-ninth year of his age.

The learned world is indebted to this sagacious and able astronomer 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 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 important 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 favourite hypothesis.

He was the first who discovered that astronomers had been mistaken in ascribing circular orbits and uniform motions to the planets, since each of them moves in an ellipsis 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 are always in the same proportion as the cubes of their mean distances from the sun. As it was long a favourite opinion of Kepler’s that there are only six primary planets, he seems to have been alarmed at the discovery made by Galileo of four new planets, or satellites of Jupiter, which gave a deathblow to the doctrines contained in his Mysterium Cosmographicum. The sagacity of this wonderful man, and his incessant application to the study of the planetary motions, pointed out to him some cf the genuine principles from which these motions originate. He considered gravity as a power that is mutual between bodies; that the earth and moon tend towards each other, and would meet in a point so many times nearer to the earth than to the moon as the earth is greater than the moon, if their motions did not prevent it. His opinion of the tides was, that they arise from the gravitation of the waters towards the moon; but his notions of the laws of motion not being accurate, he could not turn bis conceptions to the best advantage. The prediction he uttered at the end of his epitome of astronomy has been long since verified by the discoveries of Sir Isaac Newton, namely, that the determination of the true laws of gravity was reserved for the succeeding age, when the Author of nature would be pleased to reveal those mysteries.

To this concise account of the illustrious Kepler we shall now add a list of his principal publications. These are, 1. Mysterium Cosinographicum, already mentioned, 4to; 2. Paralipomena ad Vitellionem, quibus Astronomiae Pars Optica traditur, 1604, 4to; 3. De Stella Nova in Pede Serpentarii, 1606, 4to; 4. Astronomia Nova, seu Physica Caelestis, tradita Commentariis de Motibus Stellae Martis, ex Observationibus Tyconis Brahei, 1609, folio; 5. Dissertationes cum Nuncio Sidereo Galilei, 1610; 6. De Cometis libri tres, 1611, 4to; 7. Ephemerides Novae, from 1617 to 1620; 8. Epitome Astronomiae Coper-nicanae, in two volumes 8vo, the first published in 1618, and the second in 1622; 9. Harmonices Mundi, lib. v. 1619, 4to; 10. Chilias Logarithmorum in totidem numeros rotundos, 1624, 4to; 11. Supplementum Chiliadis, &c. 1625, 4to; 12. Tabuíae Rodolphinae, 1627, folio; 13. De Jesu Christi Servatoris anno natalitio. He was also the author of several pieces connected with chronology, the mensuration of solids, and trigonometry, and of a treatise on dioptrics, an excellent performance for the period in which he flourished. See the Dissertations on the History of Physical and Mathematical Science prefixed to this work.