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.