KEPLER, JOHN, was born at Well in the duchy of Wfirtcmberg, 21st of December 1571. He was a seven-mouths child, very weak and sickly, and survived with difficulty a eevero attack of smallpox.
His parents, Henry Kepler and Catherine Ouldeomann, were of noble descent, although their circumstances were far from affluent. The father, at the time of his marriage, was a petty officer in the service of the Duke of Wiirtemberg, and joined the army in the Nether lands a few years after the birth of his eldest son John. Upon his return to Germany he learnt that an acquaintance for whom he had incautiously become security had absconded, and had left him the unexpected charge of liquidating the bond. This circumstance obliged him to dispose of his house and nearly the whole of his possessions, and to become a tavero-keeper at Elmendingen. Young Kepler had been sent in the year 1577 to a school at Elmeudingen, and he con tinued there until the occurrence of the event to which we have just alluded, and which was the cause of a temporary interruption in his education, as it appears that he was taken home and employed in menial services until his twelfth year, when he returned to school. In 15S6 he was admitted into the monastic school of Maulbronn, I where the cost of his education was defrayed by the Duke of Wiirtemberg. The regulations of this school required that after remaining a year in the superior classes the students should offer themselves for examination at the college of Tubingen for the degree of Bachelor. On obtaining this degree they returned with the title of veterans ; and having completed the prescribed course of study, they were admitted as resident students at Tiibingen, whence they pro ceeded in about a year to the degree of Master. During his under graduateship Kepler's studies were much interrupted by periodical returns of the disorders which had so nearly proved fatal to him during childhood, as also by the dissensions between his parents, in consequence of which his father left his home, and soon after died abroad. Notwithstanding the many disadvantages he. must have laboured under from the above circumstances, and from the confused 'ate in which they had left his domestic affairs, Kepler took the degree of Master in August 1591, attaining the second place in the annual examination. The first name on the list was John Hippolytus Eventing.
While thus engaged at Tiibingcn, the astronomical lectureship of Gratz, the chief town in Styria, became vacant by the death of George Stadt, and the situation was offered to Kepler, who was forced to accept it by the authority of his tutors, although we have his own assurance that at that period he had given no particular attention to astronomy. This must have been in the year 1593-94. In 1596 he published his Mysterium Cosmographicum,' wherein he details the many ingenious hypotheses which he had successively formed, examined, and rejected, concerning the number, distance, and periodic times of the planets; and finally, proposes a theory which he imagines will account in a satisfactory manner for the order of the heavenly bodies, which theory rests upon the fancied analogy between the relative dimensions of the orbits of those bodies, and the diameters of circles inscribed and circumscribed about the five regular solids. lu 1597 Kepler married Barbara Muller von Muhleckh, a lady who, although two years younger than himself, was already a widow for the second time. This alliance soon involved him in difficulties,
which together with the troubled state of the province of Styria, arising out of the two great religious parties into which the empire was then divided, induced him to withdraw from Gratz into Hungary, whence he transmitted to a friend at Tubingen, several short treatises —` On the Magnet," On the Cause of the Obliquity of the Ecliptic,' and 'On the Divine Wisdom as shown in the Creation.' In 1600 Kepler, having learned that Tycho Brand was at Benach in Bohemia, and that his observations had led him to a more accurate determina tion of the eccentricities of the planets' orbits, determined on paying him a visit, and was welcomed in the kindest manlier by Tycho, by whom he was introduced the following year to the emperor, and honoured with the title of imperial mathematician, on condition of assisting Tycho in his calculations. Upon the death of Tycho, which happened in the month of October of the same year, Kepler suc ceeded him as principal mathematician to the emperor. To this great man Kepler was under many obligations, not merely for the pecuniary assistance and hospitality which himself and family so often expe rienced from Tycho, and upon which at one period they entirely depended fur subsistence, but still more for the sound advice which he gave him, to abandon speculation, and to apply himself to the deduction of causes from their observed effects,—advice which Kepler greatly needed, and to which, if he had adhered moro closely, his fame would have been even greater than what it now is. It is to bo regretted that upon several occasions the conduct of Kepler towards Tycho Brand ill-accorded with the generosity of the latter, though this appears to be attributable rather to the impetuosity of Kepler's temper, than to any want of gratitudo towards his benefactor. It has beeu eaid that Kepler was appointed imperial mathematician ou condition of assisting Tycho in hie calculations. The object of these calculations was the formation of new aArouomical tables generally, which were to be called the Itudolphine Tables, in honour of Rudolph the then emperor of Bohemia, who had promised, not merely to defray the expense of their construction, but likewise to provide Kepler with a liberal salary; neither of which his circumstances ever permitted him to fulfil. The part more particularly allotted to Kepler was the reduction of Tycho's observations relative to the planet Mars, and to this circumstance is mainly owing his grand discovery of the law of elliptic orbits, and that of the equable description of areas. The pecuniary difficulties however in which he found himself almost incessantly involved in consequence of the non payment of his salary, greatly retarded the progress of his labours, and obliged him to seek a livelihood by casting nativities. The Itudolphine Tables were therefore postponed, and he applied himself to works of a less costly character, from which ho might expect to derive more immediate remuneration. In 1602 appeared his 'Fonda mental Principles of Astrology;' in 1604 his 'Supplement to Vitellion;' in 1605 'A Letter coneerniug the Solar Eclipse ; ' and in 1606 ' An Account of the New Star which had appeared in 1604 in the Constellation Cassiopeia.' Of these the 'Supplement to Vitellion' was important, as containing the first consistent theory of that branch of optics termed dioptrics.