TO THE READER REGARDING THE HYPO-

THESES OF THIS WORK.

I do not doubt that certain learned men, now that the report of the novelty of the hypotheses In this context, "hypotheses" refers to the underlying mathematical assumptions or models used to explain planetary motion. of this work has spread—which establishes that the Earth moves and that the Sun remains immobile in the center of the universe—will be greatly offended, and think that the liberal arts, which were correctly established long ago, ought not to be thrown into confusion. But if they are willing to weigh the matter exactly, they will find that the author of this work has committed nothing that deserves blame. For it is the duty of an astronomer to collect the history of celestial motions through diligent and skillful observation. Then, he must conceive and devise causes for these motions, or hypotheses—since he cannot by any means reach the true causes—of such a kind that, if they are assumed, these same motions can be correctly calculated from the principles of geometry, both for the future and for the past. This craftsman Referring to Copernicus. has performed both of these tasks exceptionally well. For it is not necessary that these hypotheses be true, nor even likely; this one thing is sufficient: that they provide a calculation consistent with observations. Unless, perhaps, someone is so ignorant of geometry and optics that he considers the epicycle term: epicycle. A small circle whose center moves around the circumference of a larger one; used in ancient astronomy to explain the complex paths of planets. of Venus to be likely, or believes it to be the reason why Venus sometimes precedes and sometimes follows the Sun by forty degrees and more. For who does not see that, if this is assumed, it necessarily follows that the diameter of the star The author uses "star" here to refer to the planet Venus. would appear more than four times larger, and the body itself more than sixteen times larger, at perigee original Greek: "περιγειῳ" (perigeio). The point in an orbit where the planet is closest to the Earth. than at apogee original Greek: "απογειῳ" (apogeio). The point in an orbit where the planet is furthest from the Earth.? Yet the experience of every age contradicts this. There are other things in this discipline no less absurd, which there is no need to examine at present. For it is clear enough that this art is completely and simply ignorant of the causes of the apparent unequal motions. And if it devises any by imagination—as it certainly devises many—it does not devise them to persuade anyone that it is so, but only so that they may establish a correct calculation. Moreover, since various hypotheses sometimes offer themselves for one and the same motion (as in the movement of the Sun: eccentricity and the epicycle), the astronomer will seize that one which is easiest to grasp. The philosopher, perhaps, [will seek] more for likelihood... The text ends mid-sentence here; the catchword "gis rea" suggests the next page continues with "magis realem" (more real).