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Rh making two revolutions while the centre of the small epicycle moves once round the circumference of a larger one in the same direction in which the centre of the latter moves along the orbit of Saturn.

The Tychonic system did not retard the adoption of the Copernican one, but acted as a stepping-stone to the latter from the Ptolemean. By his destruction of the solid spheres of the ancients and by the thorough discomfiture of the scholastics caused by this and other results of his observations of comets, he helped the Copernican principle onward far more effectually than he could have done by merely acquiescing in the imperfectly formed system, which the results of his own observations were to mould into the beautiful and simple system which is the foundation of modern astronomy.

The book on the comet of 1577 was ready from the press in 1588, and though not regularly published as yet, copies were sent to friends and correspondents whenever an opportunity offered. Thus Tycho's pupil, Gellius Sascerides, who in the summer of 1588 started on a journey to Germany, Switzerland, and Italy, brought copies to Rothmann and Maestlin, to whom he was also the bearer of letters. The Landgrave did not receive a copy, but studied Rothmann's copy with great interest, and thought that it must have been meant for himself, until Rothmann suggested that it was only part of an unfinished work, and that he would get one later on, which of course he did as soon as Tycho heard of this incident. In the following year, while he was at the fair of Frankfurt, Gellius received another copy of the book, which he was to bring to Bologna to Magini, and this