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 among the troops of Wittemberg, 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 Tübingen, 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 calam-
ties 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 Rodolph, 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 darling 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 al-
Keratophy-ways in the same proportion as the cubes of their mean
tom. distances from the sun." As it was long a favourite
Kerkrio. opinion of Kepler's, that there are only six primary plan-
ets, 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 con-
tained 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 of 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 accu-
rate, he could not turn his thoughts to the best advan-
tage. The prediction he uttered at the end of his epi-
tome of astronomy, has been long since verified by the
discoveries of Sir Isaac Newton, that the discovery of
such things (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 celebrated Kepler, we
shall now add a list of his principal publications. Mys-
terium Cosmographicum, already mentioned, 410; Pa-
ralipomena ad Vitellionem, quibus Astronomia Pars Op-
tica traditur, 1624, 410; De Stella Nova in Pede Ser-
pentarii, 1626, 410; Astronomia Nova, seu Physica Cæ-
lestis, tradita Commentariis de Motibus Stella Martis, ex
Observationibus Tyconii Braheii, 1609, folio; Differen-
tiones cum Nuncio Sidereo Galilei, 1610; De Cometis,
Libri tres, 1611, 410; Ephemerides Novæ, from 1617
to 1620; Epitome Astronomiæ Copernicanæ, in two vol-
umes 8vo, the first published in 1618, and the second
in 1622; Harmonices Mundi, lib. v. 1619, 410; Chri-
stias Logarithmorum in totidem numeros rotundos,
1624, 410; Supplementum Chiliadit, &c. 1625, 410;
Tabule Rodolphine, 1627, folio; De Jesu Christi Ser-
vatoris anno natalitio, &c. He was also the author of
several other pieces connected with chronology, the
mensuration of solids, and trigonometry, with a treatise
on dioptrics, an excellent performance for the period
in which he flourished.