The matter contained in this sketch of Kepler’s history, is exclusively derived from the Life published in the Library of Useful Knowledge. To that work we refer all readers who wish to make themselves acquainted with the contents of Kepler’s writings, and with the singular methods by which he was led to his great discoveries: it will be evident, on inspection, that it would be useless to attempt farther compression of the scientific matter therein contained. Our object therefore will be to select such portions as may best illustrate his singular and enthusiastic mind, and to give a short account of his not uneventful life.

John Kepler was born December 21, 1571, Long. 29° 7´, Lat. 48° 54´, as we are carefully informed by his earliest biographer Hantsch. It is well to add that on the spot thus astronomically designated as our astronomer’s birth-place, stands the city of Weil, in the Duchy of Wirtemberg. Kepler was first sent to school at Elmendingen, where his father, a soldier of honourable family, but indigent circumstances, kept a tavern: his education was completed at the monastic school of Maulbronn, and the college of Tubingen, where he took his Master’s degree in 1591. About the same time he was offered the astronomical lectureship at Gratz, in Styria: and he accepted the post by advice, and almost by compulsion, of his tutors, “better furnished,” he says, “with talent than knowledge, and with many protestations that I was not abandoning my claim to be provided for in some other more brilliant profession.” Though well skilled in mathematics, and devoted to the study of philosophy, he had felt hitherto no especial vocation to astronomy, although he had become strongly impressed with the truth of the Copernican system, and had defended it publicly in the schools of Tubingen. He was much engrossed by inquiries of a very different character: and it is fortunate for his fame that circumstances withdrew him from the mystical pursuits to which through life he was more or less addicted; from such profitless toil as the “examination of the nature of heaven, of souls, of genii, of the elements, of the essence of fire, of the cause of fountains, of the ebb and flow of the tide, the shape of the continents and inland seas, and things of this sort,” to which, he says, he had devoted much time. The sort of spirit in which he was likely to enter on the more occult of these inquiries, and the sort of agency to which he was likely to ascribe the natural phenomena of which he speaks, may be estimated from an opinion which he gravely advanced in mature years and established fame, that the earth is an enormous living animal, with passions and affections analogous to those of the creatures which live on its surface. “The earth is not an animal like a dog, ready at every nod; but more like a bull or an elephant, slow to become angry, and so much the more furious when incensed.” “If any one who has climbed the peaks of the highest mountains throw a stone down their very deep clefts, a sound is heard from them; or if he throw it into one of the mountain lakes, which beyond doubt are bottomless, a storm will immediately arise, just as when you thrust a straw into the ear or nose of a ticklish animal, it shakes its head, and runs shuddering away. What so like breathing, especially of those fish who draw water into their mouths, and spout it out again through their gills, as that wonderful tide! For although it is so regulated according to the course of the moon, that in the preface to my ‘Commentaries on Mars’ I have mentioned it as probable that the waters are attracted by the moon, as iron is by the loadstone, yet if any one uphold that the earth regulates its breathing according to the motion of the sun and moon, as animals have daily and nightly alternations of sleep and waking, I shall not think his philosophy unworthy of being listened to; especially if any flexible parts should be discovered in the depths of the earth to supply the functions of lungs or gills.”

The first fruit of Kepler’s astronomical researches was entitled ‘Prodromus Dissertationis CosmographicÆ,’ the first part of a work to be called ‘Mysterium Cosmographicum,’ of which, however, the sequel was never written. The most remarkable part of the book is a fanciful attempt to show that the orbits of the planets may be represented by spheres circumscribed and inscribed in the five regular solids. Kepler lived to be convinced of the total baselessness of this supposed discovery, in which, however, at the time, he expressed high exultation. In the same work are contained his first inquiries into the proportion between the distances of the planets from the sun and their periods of revolution. He also attempted to account for the motion of the planets, by supposing a moving influence emitted like light from the sun, which swept round those bodies, as the sails of a windmill would carry any thing attached to them: of a genuine central force he had no knowledge, though he had speculated on the existence of an attractive force in the centre of motion, and rejected it on account of difficulties which he could not explain. The ‘Prodromus’ was published in 1596, and the genius and industry displayed in it gained praise from the best astronomers of the age.

In the following year Kepler withdrew from Gratz into Hungary, apprehending danger from the unadvised promulgation of some, apparently religious, opinions. During this retirement he became acquainted with the celebrated Tycho Brahe, at that time retained by the Emperor Rodolph II. as an astrologer and mathematician, and residing at the castle of Benach, near Prague. Kepler, harassed throughout life by poverty, was received by his more fortunate fellow-labourer with cordial kindness. No trace of jealousy is to be found in their intercourse. Tycho placed the observations which he had made with unremitted industry during many years in the hands of Kepler, and used his interest with the Emperor to obtain permission for his brother astronomer to remain at Benach as assistant observer, retaining his salary and professorship at Gratz. Before all was settled, however, Kepler finally threw up that office, and remained, it should seem, entirely dependent on Tycho’s bounty. The Dane was then employed in constructing a new set of astronomical tables, to be called the Rudolphine, intended to supersede those calculated on the Ptolemaic and Copernican systems. He was interrupted in this labour by death, in 1601; and the task of finishing it was intrusted to Kepler, who succeeded him as principal mathematician to the Emperor. A large salary was attached to this office, but to extract any portion of it from a treasury deranged and almost exhausted by a succession of wars, proved next to impossible. He remained for several years, as he himself expresses it, begging his bread from the Emperor at Prague, during which the Rudolphine Tables remained neglected, for want of funds to defray the expenses of continuing them. He published, however, several smaller works; a treatise on Optics, entitled a Supplement to Vitellion, in which he made an unsuccessful attempt to determine the cause and the laws of refraction; a small work on a new star which appeared in Cassiopeia in 1604, and shone for a time with great splendour; another on comets, in which he suggests the possibility of their being planets moving in straight lines. Meanwhile he was continuing his labours on the observations of Tycho, and especially on those relating to the planet Mars: and the result of them appeared in 1609, in his work entitled ‘Astronomia Nova;’ or Commentaries on the motions of Mars. He engaged in these extensive calculations from dissatisfaction with the existing theories, by none of which could the observed and calculated motions of the planets be made to coincide; but without any notion whither the task was about to lead him, or of rejecting the complicated machinery of former astronomers—

His inquiries are remarkable for the patience with which he continued to devise hypotheses, one after another, and the scrupulous fidelity with which he rejected them in succession, as they proved irreconcileable with the unerring test of observation. Not less remarkable is the singular good fortune by which, while groping in the dark among erroneous principles and erroneous assumptions, he was led, by careful observation of Mars, to discover the true form of its orbit, and the true law of its motion, and the motion of all planets, round the sun. These are enunciated in two of the three celebrated theorems known by the name of Kepler’s Laws, beyond comparison the most important discoveries made in astronomy from the time of Copernicus to that of Newton, of which the first is, that the planets move in ellipses, in one of the foci of which the sun is placed the second, that the time of describing any arc is proportional, in the same orbit, to the area comprised by the arc itself, and lines drawn from the sun to the beginning and end of it.

About the year 1613 Kepler quitted Prague, after a residence of eleven years, to assume a professorship in the University of Linz. The year preceding his departure saw him involved in great domestic distress. Want of money, sickness, the occupation of the city by a turbulent army, the death of his wife and of the son whom he best loved, these, he says to a correspondent, “were reasons enough why I should have overlooked not only your letter, but even astronomy itself.” His first marriage, contracted early in life, had not been a happy one: but he resolved on a second venture, and no less than eleven ladies were successively the objects of his thoughts. After rejecting, or being rejected, by the whole number, he at last settled on her who stood fifth in the list; a woman of humble station, but, according to his own account, possessed of qualities likely to wear well in a poor man’s house. He employed the judgment and the mediation of his friends largely in this delicate matter: and in a letter to the Baron Strahlendorf, he has given a full and amusing account of the process of his courtships, and the qualifications of the ladies among whom his judgment wavered. He proposed to one lady whom he had not seen for six years, and was rejected: on paying her a visit soon after, he found, to his great relief, that she had not a single pleasing point about her. Another was too proud of her birth; another too old; another married a more ardent lover, while Kepler was speculating whether he would take her or not; and a fifth punished the indecision which he had shown towards others by alternations of consent and denial, until after a three months’ courtship, the longest in the list, he gave her up in despair.

Kepler did not long hold his professorship at Linz. Some religious opinions relative to the doctrine of transubstantiation gave offence to the Roman Catholic party, and he was excommunicated. In 1617 he received an invitation to fill the chair of mathematics at Bologna: this however he declined, pleading his German origin and predilections, and his German habits of freedom in speech and manners, which he thought likely to expose him to persecution or reproach in Italy. In 1618 he published his Epitome of the Copernican system, a summary of his philosophical opinions, drawn up in the form of question and answer. In 1619 appeared his celebrated work ‘Harmonice Mundi,’ dedicated to King James I. of England; a book strongly illustrative of the peculiarities of Kepler’s mind, combining the accuracy of geometric science with the wildest metaphysical doctrines, and visionary theories of celestial influences. The two first books are almost strictly geometrical; the third treats of music; for the fourth and fifth, we take refuge from explaining their subjects in transcribing the author’s exposition of their contents. “The fourth, metaphysical, psychological, and astrological, on the mental essence of harmonies, and of their kinds in the world, especially on the harmony of rays emanating on the earth from the heavenly bodies, and on their effect in nature, and on the sublunary and human soul; the fifth, astronomical and metaphysical, on the very exquisite harmonies of the celestial motions, and the origin of the eccentricities in harmonious proportions.” This work, however, is remarkable for containing amid the varied extravagances of its two last books, the third of Kepler’s Laws, namely, that the squares of the periods of the planets’ revolution vary as the cubes of their distances from the sun; a discovery in which he exulted with no measured joy. “It is now eighteen months since I got the first glimpse of light, three months since the dawn, very few days since the unveiled sun, most admirable to gaze upon, burst out upon me. Nothing holds me; I will indulge in my sacred fury; I will triumph over mankind by the honest confession that I have stolen the golden vases of the Egyptians, to build up a tabernacle for my God far away from the confines of Egypt. If you forgive me, I rejoice; if you are angry, I can bear it: the die is cast, the book is written; to be read either now or by posterity, I care not which: it may well wait a century for a reader, as God has waited six thousand years for an observer.”

The substance of Kepler’s astrological opinions is contained in this work. It is remarkable that one whose candour and good faith are so conspicuous, one so intent on correcting his various theories by observation and experience, should have given in to this now generally rejected system of imposture and credulity; nay should profess to have been forced to adopt it from direct and positive observations. “A most unfailing experience (as far as can be hoped in natural phenomena), of the excitement of sublunary nature by the conjunctions and aspects of the planets, has instructed and compelled my unwilling belief.” At the same time he professed through life a supreme contempt for the common herd of nativity casters, and claimed to be the creator of a “new and most true philosophy, a tender plant which, like all other novelties, ought to be carefully nursed and cherished.” His plant was rooted in the sand, and it has perished; nor is it important to explain the fine-spun differences by which his own astrological belief was separated from another not more baseless. Poor through life, he relieved his ever recurring wants by astrological calculations: and he enjoyed considerable reputation in this line, and received ample remuneration for his predictions. It was principally as astrologers that both Tycho Brahe and Kepler were valued by the Emperor Rudolph: and it was in the same capacity that the latter was afterwards entertained by Wallenstein. One circumstance may suggest a doubt whether his predictions were always scrupulously honest. From the year 1617 to 1620, he published an annual Ephemeris, concerning which he writes thus: “In order to pay the expense of the Ephemeris for these two years, I have also written a vile prophesying almanac, which is hardly more respectable than begging; unless it be because it saves the Emperor’s credit, who abandons me entirely, and, with all his frequent and recent orders in council, would suffer me to perish with hunger.” Poverty is a hard task-master; yet Kepler should not have condescended to become the Francis Moore of his day.

In 1620, Kepler was strongly urged by Sir Henry Wotton, then ambassador to Venice, to take refuge in England from the difficulties which beset him. This invitation was not open to the objections which had deterred him from accepting an appointment in Italy: but love of his native land prevailed to make him decline it also. He continued to weary the Imperial Government with solicitations for money to defray the expense of the Rudolphine Tables, which were not printed until 1627. These were the first calculated on the supposition of elliptic orbits, and contain, besides tables of the sun and planets, logarithmic and other tables to facilitate calculation, the places of one thousand stars as determined by Tycho, and a table of refractions. Similar tables of the planetary motions had been constructed by Ptolemy, and reproduced with alterations in the thirteenth century under the direction of Alphonso, King of Castile. Others, called the Prussian Tables, had been calculated after the discoveries of Copernicus, by two of that great astronomer’s pupils. All these, however, were superseded in consequence of the observations of Tycho Brahe, observations far more accurate than had ever before been made: and for the publication of the Rudolphine Tables alone, which for a long time continued unsurpassed in exactness, the name of Kepler would deserve honourable remembrance.

Kepler was the first of the Germans to appreciate and use Napier’s invention of logarithms: and he himself calculated and published a series, under the title ‘Chilias Logarithmorum,’ in 1624. Not long after the Rudolphine Tables were printed, he received permission from the Emperor Ferdinand to attach himself to the celebrated Wallenstein, a firm believer in the science of divination by the stars. In him Kepler found a more munificent patron than he had yet enjoyed; and by his influence he was appointed to a professorship at the University of Rostock, in the Duchy of Mecklenburgh. But the niggardliness of the Imperial Court, which kept him starving through life, was in some sense the cause of his death. He had claims on it to the amount of eight thousand crowns, which he took a journey to Ratisbon to enforce, but without success. Fatigue or disappointment brought on a fever which put an end to his life in November, 1630, in his 59th year. A plain stone, with a simple inscription, marked his grave in St. Peter’s church-yard, in that city. Within seventy paces of it, a marble monument has been erected to him in the Botanic Garden, by a late Bishop of Constance. He left a wife and numerous family ill provided for. His voluminous manuscripts are now deposited in the Imperial Library of St. Petersburg. Only one volume of letters, in folio, has been published from them; and out of these the chief materials for his biography have been extracted.