On the Revolutions of the Heavenly Spheres

And I found indeed in Cicero, first, that Nicetus had thought the earth moved. Afterwards, I also found in Plutarch that some others had been of that opinion, whose words I have decided to transcribe here so that they may be accessible to everyone: "Some others say that the earth remains still, but Philolaus the Pythagorean says that it moves in a circle around the fire the central fire in an oblique circle, in the same way as the Sun and Moon. Heraclides of Pontus and Ecphantus the Pythagorean do not indeed move the earth from place to place, but by causing it to rotate like a wheel, girded from west to east, around its own center."

Having found the occasion, I began to think about the mobility of the earth. And although the opinion seemed absurd, yet because I knew that this liberty had been granted to others before me to imagine whatever circles they pleased in order to demonstrate the phenomena of the stars, I thought that I might also be easily permitted to experiment whether, by assuming some motion of the earth, stronger demonstrations than theirs could be found in the revolution of the celestial spheres.

And so, having posited the motions that I attribute to the earth later in this work, through much and long observation I finally found that if the motions of the other wandering stars are compared to the circulation of the earth and are calculated for the revolution of each star, not only do their phenomena follow from that, but also the order and magnitudes of all the stars and spheres, and the heaven itself is so connected that nothing in any part of it can be transposed without causing confusion in the remaining parts and the whole universe. Therefore, I have also followed this order in the progress of the work, that in the first book I describe all the positions of the spheres, along with the motions I attribute to the earth, so that this book may contain, as it were, the general constitution of the universe. In the remaining books, I afterwards compare the motions of the remaining stars and all the spheres with the mobility of the earth, so that it may be inferred to what extent the motions and appearances of the remaining stars and spheres can be reconciled if they are compared to the motions of the earth. Nor do I doubt that ingenious and learned mathematicians will agree with me if they are willing to know and weigh, not superficially, but thoroughly, those things which I bring forth in this work for the demonstration of these matters. And so that learned and unlearned alike may see that I do not shrink from the judgment of anyone at all,