Cotemporary with Tycho Brahé and Galileo, and to some extent the
associate and successor of the former, was John Kepler, one of the
most eminent astronomers who have appeared in any age, and to whom the
science is indebted for much of its present perfection. He was born
December 27, 1571, at Wiel in Wurtemberg, and was descended of a noble
but reduced family. His father, originally an officer of distinction
in the army of Wurtemberg, was, at the time of young Kepler’s birth,
in the humble capacity of a small inn-keeper; and thus, as is too
often the case with genius, our philosopher had to struggle into fame
through poverty and the vicissitudes of his father’s fortune. Poor,
unbefriended, of a weakly constitution, and one of the most diminutive
of children, Kepler received the rudiments of knowledge at the
Monastic school of Maulbrunn, where he gave early indications of
talent, and of that irrepressible spirit which, amid the severest
obstructions, was never diverted from the main object of its pursuit.
After his father’s death, which took place in his eighteenth year, he
left Maulbrunn, and succeeded in entering the college of Tubingen.
Here he completed the course of study then prescribed――first
philosophy and mathematics, and then theology; taking the degree of
Bachelor in the year 1588, and that of Master of Philosophy in the
year 1591. Of apt inquiring powers as a divine, and of more than
average eloquence as a preacher, Kepler could now have readily
succeeded in the church; but mathematics and the exact sciences were
his favorite themes; and it may be fairly questioned if ever he turned
a single thought to the clerical profession, beyond what the
curriculum of the university compelled. In 1593-4, his reputation as a
geometrician had so increased, that he was invited to fill the
mathematical chair in the university of Gratz, in Styria. Here he
pursued his astronomical studies with the most commendable zeal,
devoting himself especially to the investigation of the physical
causes of the motion of the celestial bodies.
Shortly after his installment, he married a lady descended from a
noble family, and was beginning to enjoy that domestic happiness and
studious quiet so congenial to his wishes, when persecution on account
of his religion compelled him to leave Gratz, to which, however, he
was afterwards recalled by the states of Styria. Meanwhile Tycho
Brahé, who had come to Germany, and was comfortably settled under the
munificent patronage of Rodolphus, fixed upon Kepler as a suitable
assistant, and soon induced him, by urgent letters and flattering
promises, to accept of the situation. Compelled in a great measure by
the unsettled state of affairs in Austria, Kepler speedily repaired to
Prague, and applied himself, in conjunction with Tycho, to the
completion of the Rodolphine Tables, which were first published at Ulm
in 1626. At Tycho’s recommendation, he was established at that place;
but as his office and science did not afford him a subsistence, he
studied medicine, in order to gain a livelihood by its practice. The
emperor had assigned him a salary, but in the period of trouble which
preceded the Thirty Years’ War, it was not paid. Even when he was
appointed imperial mathematician by Matthias, Rodolphus’ successor,
his hopes of recovering his arrears were disappointed. Fresh
controversies with the clergy, and the disturbed state of the country,
made his situation very uncomfortable: he therefore left Lintz,
repaired to Ratisbon, declined an invitation to England, was confirmed
by the succeeding emperor, Ferdinand, in the office of imperial
methematician, and afterwards went to Ulm to superintend the printing
of the Rodolphine Tables. In 1627 he returned to Prague, and received
from the emperor six thousand guilders. He finally became a professor
at Rostock, on the recommendation of Albert, duke of Wallenstein, but
did not receive the promised compensation. In 1630 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, in the fifty-ninth year of
his age. In 1808, a monument, consisting of a Doric temple enshrining
his bust, was erected to his memory in Ratisbon by Charles Theodore
Von Dalberg.
Kepler is represented by his biographers as a man of small stature,
thin, of a weak constitution, and defective sight; but of somewhat gay
and sportive manners. He was attached to his science with the most
fervent enthusiasm; he sought after truth with eagerness, but forgot,
in the search, the maxims of worldly prudence. To him were allotted
but a scanty share of what are commonly esteemed the pleasures of
life; but he endured all calamities with firmness, being consoled by
the higher enjoyments which science never fails to impart to her true
and cordial votaries. ‘As an astronomer,’ says Lalande, ‘he is as
famous in astronomy for the sagacious application which he made of
Tycho’s numerous observations (for he was not himself an observer), as
the Danish philosopher for the collection of such vast materials.’ To
him, says another authority, the world is indebted 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 though this led him to the adoption of
strange and ridiculous conceits, we shall readily be disposed to
overlook these, when we reflect they were the means of leading him to
the most important discoveries. 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 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 are always in the same
portion as the cubes of their mean distances from the sun. 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
toward 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 his 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 these mysteries.