[Note 16\5: See Venturi, _Essai sur les Ouvrages Physico-Mathématiques de Leonard da Vinci, avec des Fragmens tirés de ses Manuscrits apportés d'Italie_. Paris, 1797; and, as there quoted, _Marini Archiatri Pontificii_, tom. ii. p. 251.] Leonardo da Vinci, who was an eminent mathematician, as well as painter, about 1510, explained how a body, by describing a kind of spiral, might descend towards a revolving globe, so that its apparent motion relative to a point in the surface of the globe, might be in a {271} straight line leading to the centre. He thus showed that he had entertained in his thoughts the hypothesis of the earth's rotation, and was employed in removing the difficulties which accompanied this supposition, by means of the consideration of the composition of motions. In like manner we find the question stirred by other eminent men. Thus John Muller of Konigsberg, a celebrated astronomer who died in 1476, better known by the name of Regiomontanus, wrote a dissertation on the subject "Whether the earth be in motion or at rest," in which he decides _ex professo_[17\5] against the motion. Yet such discussions must have made generally known the arguments for the heliocentric theory. [Note 17\5: Schoneri _Opera_, part ii. p. 129.] We have already seen the enthusiasm with which Rheticus, who was Copernicus's pupil in the latter years of his life, speaks of him. "Thus," says he, "God has given to my excellent preceptor a reign without end; which may He vouchsafe to guide, govern, and increase, to the restoration of astronomical truth. Amen." Of the immediate converts of the Copernican system, who adopted it before the controversy on the subject had attracted attention, I shall only add **Mæstlin, and his pupil, Kepler. **Mæstlin published in 1588 an _Epitome Astronomiæ_, in which the immobility of the earth is asserted; but in 1596 he edited Kepler's _Mysterium Cosmographicum_, and the _Narratio_ of Rheticus: and in an epistle of his own, which he inserts, he defends the Copernican system by those physical reasonings which we shall shortly have to mention, as the usual arguments in this dispute. Kepler himself, in the outset of the work just named, says, "When I was at Tübingen, attending to Michael Mæstlin, being disturbed by the manifold inconveniences of the usual opinion concerning the world, I was so delighted with Copernicus, of whom he made great mention in his lectures, that I not only defended his opinions in our disputations of the candidates, but wrote a thesis concerning the First Motion which is produced by the revolution of the earth." This must have been in 1590.