AUTHOR’S PREFACE.

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...they might be able to demonstrate and observe your magnitude. Next, in establishing the motions of these, as well as the other five wandering stars The "wandering stars" or planetae known at the time: Mercury, Venus, Mars, Jupiter, and Saturn., they do not use the same principles and assumptions, nor the same demonstrations of the apparent revolutions and motions. For some use only homocentric circles Also called concentric circles; a system where all celestial spheres share the Earth as their exact center., others use eccentrics and epicycles Mathematical devices where a planet moves on a small circle (epicycle) which itself moves along a larger circle (deferent) that is slightly off-center from the Earth (eccentric)., yet they still do not fully achieve what they seek. For those who relied on homocentric circles, although they demonstrated that several different motions could be composed from them, they were nonetheless unable to establish anything certain that would truly correspond to the phenomena The observed positions and movements of the stars and planets as seen from Earth..

However, those who devised eccentrics, although they seem for the most part to have resolved the apparent motions with consistent numerical calculations, have nonetheless admitted many things in the meantime which seem to contravene the first principles concerning the uniformity of motion The ancient Greek requirement that all celestial motion must be perfectly circular and uniform (at a constant speed).. They were also unable to find or deduce the most important thing—namely, the form of the world and the certain symmetry of its parts.

Instead, it happened to them just as if someone were to take hands, feet, a head, and other limbs from different places—drawn very well indeed, but not in comparison to a single body—and since they do not correspond to each other in any way, a monster rather than a human would be composed from them. Thus, in the process of demonstration, which they call a methodos original: "μέθοδον"; a systematic way of teaching or investigating., they are found to have either passed over something necessary or admitted something alien and completely irrelevant to the matter. This would least of all have happened to them if they had followed certain principles. For if the hypotheses they assumed were not fallacious, everything which follows from them would undoubtedly be verified. Although these things I am saying now may be obscure, they will become clearer in their proper place.

Therefore, when I had long pondered this uncertainty of the mathematical traditions regarding the calculation of the motions of the spheres of the world, I began to be weary that no more certain system for the motions of the machine of the world A common Renaissance metaphor for the universe as a complex, God-designed mechanism.—which was built for our sake by the best and most orderly Creator of all—was available to philosophers, who otherwise scrutinize the most minute things of this world so exquisitely. For this reason, I took it upon myself to reread the books of all the philosophers I could obtain, to investigate whether anyone had ever thought that there were other motions...