Anna Maria. The eldest of these, Susanna, was married a few months before her father's death to Jacob Bartschius, his pupil, who was educated as a physician; and his son Louis died in 1663, while practising medicine at Konigsberg. The children by his second wife are said to have died young. They were left in very narrow circumstances; and though 24,000 florins were due to Kepler by the emperor, yet only a part of this sum was received by Susanna, in consequence of her refusing to give up Tycho's Observations till the debt was paid. Kepler composed a little work entitled "The Dream of John Kepler, or Lunar Astronomy," the object of which was to describe the phenomena seen from the moon; but he died while he and Bartschius were engaged in its publication, and Bartschius having resumed the task, died also before its completion. Louis Kepler dreaded to meddle with a work which had proved so fatal to his father and his brother-in-law, but this superstitious feeling was overcome, and the work was published at Frankfort in 1636.

CHAPTER IV.

Number of Kepler's published Works.-His numerous Manuscripts in 22 folio Volumes.-Purchased by Hevelius, and afterward by Hansch, who publishes Kepler's Life and Correspondence at the Expense of Charles VI.-The History of the rest of his Manuscripts, which are deposited in the Library of the Academy of Sciences at St. Petersburg. -General Character of Kepler.-His Candour in acknowledging his Errors.-His Moral and Religious Character.His Astrological Writings and Opinions considered.-His Character as an Astronomer and a Philosopher.-The Splendour of his Discoveries.-Account of his Methods of Investigating Truth.

ALTHOUGH the labours of Kepler were frequently interrupted by severe and long-continued indisposition, as well as by the pecuniary embarrassments in which he was constantly involved, yet the ardour and power of his mind enabled him to surmount all the difficulties of his position. Not only did he bring to a successful completion the leading inquiries which he had begun, but he found leisure for composing an immense number of works more or less connected with the subject of his studies. Be tween 1594, when he published his Calendar at Gratz, and 1630, the year of his death, he publish

ed no fewer than thirty-three separate works; and he left behind him twenty-two volumes of manu. scripts, seven of which contain his epistolary correspondence.

The celebrated astronomer Hevelius, who was a contemporary of Louis Kepler, purchased all these manuscripts from Kepler's representatives. At the death of Hevelius they were bought by M. Gottlieb Hansch, a zealous mathematician, who was desirous of giving them to the world. For this purpose he issued a prospectus in 1714 for publishing them by subscription, in 22 volumes folio; but this plan having failed, he was introduced to Charles VI., who liberally obtained for him 1000 ducats to defray the expense of the publication, and an annual pension of 300 florins. With such encouragement, Hansch published in 1718, in one volume folio, the correspondence of Kepler, enti tled "Epistolæ ad Joannem Keplerum, insertis ad easdem responsionibus Keplerianis, quidquid hactenus reperiri potuerunt, opus novum, et cum Jo. Kepleri vita."

The expenses of this volume unfortunately exhausted the 1000 ducats which had been granted by the emperor, and, instead of being able to publish the rest of the MSS., Hansch was under the necessity of pledging them for 828 florins. Under these difficulties he addressed himself in vain to the cel

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ebrated Wolfius, to the Royal Society of London, and to other bodies that were likely to interest themselves in such a subject. In 1761, when M. De Murr, of Nuremberg, was in London, he made great exertions to obtain the MSS., and Dr. Bradley is said to have been on the eve of purchasing them. The competition probably raised the demands of the proprietor, in whose hands they continued for many years. In 1773 they were offered for 4000 francs, and some time afterward M. De Murr purchased them for the Imperial Academy of Sciences at St. Petersburg, in whose library they still remain. Euler, Lexell, and Kraft undertook the task of examining them, and selecting those that were best fitted for publication, but we believe that no steps have yet been taken for executing this task, nor are we aware that science would derive any advantage from its completion.

Although, in drawing his own character, Kepler describes himself as “troublesome and choleric in politics and doméstic matters," yet the general events of his life indicate a more peaceful disposi<tion than might have been expected from the peculiarities of his mind and the ardour of his temper(ament. On one occasion, indeed, he wrote a vio lent and reproachful letter to Tycho, who had giv en him no just ground of offence; but the state of Kepler's health at that moment, and the necessitous

circumstances in which he had been placed, present some palliation of his conduct. But, independent of this apology, his subsequent conduct was so truly noble as to reconcile even Tycho to his penitent friend. Kepler quickly saw the error which he committed; he lamented it with genuine contri. ' tion, and was anxious to remove any unfavourable › impression which he might have given of his friend; by the most public confession of his error, and by the warmest acknowledgments of the kindness of Tycho.

In his relations with the scientific men of his own times, Kepler conducted himself with that candour and love of truth which should always distinguish the philosopher. He was never actuated. by any mean jealousy of his rivals. He never scrupled to acknowledge their high merits; and when the discoveries made by the telescope established beyond a doubt the errors of some of Kepler's views, he willingly avowed his mistake, and never joined in the opposition which was made by many of his friends to the discoveries of Galileo.' A striking example of this was exhibited in reference to his supposed discovery of Mercury on the sun's disk. In the year 1607* Kepler observed

It is said that Kepler saw this dark spot while looking at the sun in a camera obscura. As a camera obscura is actual-' ly a telescope, magnifying objects in proportion to the focal

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