28 CLASSICS OF MODERN SCIENCE 

 is slow as if its earthly origin thereby showed itself. The circular 

 motion, on the other hand, is always regular, because it is not subject 

 to an intermittent cause. Those other objects, however, would cease 

 to be either light or heavy in respect to their natural movement if they 

 reached their own place, and thus they would fit into that movement. 

 Therefore if the circular movement is to be ascribed to the universe 

 as a whole and the rectilinear to the parts, we might say that the revo- 

 lution is to the straight line as the natural state is to sickness. That 

 Aristotle divided motion into three sorts, that from the center out, that 

 inward toward the center, and that around about the center, appears 

 to be merely a logical convenience, just as we distinguish point, line 

 and surface, although one cannot exist without the others, and none 

 of them are found apart from bodies. This fact is also to be consid- 

 ered, that the condition of immovability is held to be nobler and more 

 divine than that of change and inconstancy, which latter therefore 

 should be ascribed rather to the earth than to the universe, and I 

 would add also that it seems inconsistent to attribute motion to the 

 containing and locating element rather than to the contained and lo- 

 cated object, which the earth is. Finally since the planets plainly are 

 at one time nearer and at another time farther from the earth, it would 

 follow, on the theory that the universe revolves, that the movement of 

 the one and same body which is known to take place about a center, 

 that is the center of the earth, must also be directed toward the cen- 

 ter from without and from the center outward. The movement about 

 the center must therefore be made more general, and it suffices if that 

 single movement be about its own center. So it appears from all 

 these considerations that the movement of the earth is more probable 

 than its fixity, especially in regard to the daily revolution, which is 

 most peculiar to the earth. 



