GALILEO GALILEI 41 



greateir movement in relation to the chest, than the whole journey of 

 2,000 miles which they undergo in common. 



Therefore, since plainly the motion which many movable bodies 

 undergo in common is without effect and, with regard to their mutual 

 position toward one another, it is as if it did not exist, for there is no 

 change among them ; and since it only affects the relative position of 

 such bodies as do not share in the movement, for in this case the 

 mutual relation is changed ; since we have divided the universe into 

 two parts, of which one must be movable and the other immovable; 

 then for all purposes this movement will be of the same effect whether 

 it is ascribed to the earth alone or to all the rest of the universe. For 

 the working of such a motion is on nothing but the relative position 

 in which the earth and the heavenly bodies stand to one another, and 

 aside from this relative position nothing changes. If now it is in- 

 different for accomplishing this result whether the earth alone moves 

 and the whole universe rests, or the earth rests and the whole universe 

 is subject to one common movement, who can believe that Nature — 

 who by common agreement does not employ great means when she 

 can obtain the same result by smaller ones — would have undertaken 

 to set in motion an immeasurable number of mighty bodies, and that 

 with incredible velocity, to accomplish what could be obtained by the 

 moderate motion of one single body around the center? 



SiMPL. : I do not agree that that mighty movement would be 

 as if it did not happen in regard to the sun, the moon, the innumerable 

 host of fixed stars. Do you call it nothing that the sun goes from one 

 meridian to another, rises from one horizon, sinks under another, 

 brings now day, now night ; that the moon goes through similar 

 changes and likewise the other planets, as well as the fixed stars ? 



Salv. : All the changes mentioned by you are such only with 

 respect to the earth. To demonstrate this, only imagine yourself 

 away from the earth; there is then no rising or setting of the sun, 

 no horizons, no meridians, no day, no night ; in a word, by the move- 

 ment mentioned no change in the relation of the moon to the sun or 

 to any other star is evoked. All these changes have reference to the 

 earth; they are supposed only because the sun is first visible in 

 China, then Egypt, Greece, France, Spain, America, and so on, and 

 so also for the moon and the other heavenly bodies. The same proc- 



