40 CLASSICS OF MODERN SCIENCE 



smallness of the earth, which is contained in that several milHon times, 

 and therefore regard the velocity of motion which would be necessary 

 for an entire revolution in the course of a day and night, I am unable 

 to understand how any one could hold it more reasonable and credible 

 that it is this whole stellar sphere that moves and that the earth 

 remains still. 



Sagr. : Even if universal phenomena which depend upon these 

 movements could be explained as readily by the one hypothesis as by 

 the other, yet by the first general impression I would regard as more 

 unreasonable the view that the whole universe moves; just as if any 

 one should climb to the top of your dome for the purpose of getting 

 a view of the city and its environs and then should demand that the 

 whole region be made to move around him to save him the trouble of 

 turning his head. In any event, there would have to be great advan- 

 tages connected with this theory, which were lacking in the other, 

 in order that such an absurdity should be balanced and outweighed 

 and should appear more credible than the opposite opinion. But 

 Aristotle, Ptolemaus, and Signore Simplicio must find such advan- 

 tages in their theory, and I should be glad if we might hear these 

 advantages if they exist, or if they do not, that some one would ex- 

 plain to me why they do not and cannot exist. 



Salv. : If , in spite of every sort of investigation, I am able to find 

 no such differences, I believe I have thereby discovered that such 

 difference does not exist. So in my opinion it is useless to pursue this 

 further : rather let us proceed. Motion is only so far motion and acts 

 as such, if it stands in relation to things which lack motion. In re- 

 lation to things that are all in the same degree affected by it, it is as 

 much without effect as if it did not take place. The wares with which 

 a ship is loaded move, when they depart from Venice and arrive at 

 Aleppo, passing Korf u, Candia, Cyprus etc ; since Venice, Korf u and 

 Candia remain fixed and do not move with the ship. But in respect 

 to the bales, chests, and other pieces of baggage which are on the ship 

 as cargo or ballast, the movement of the ship itself from Venice to 

 Syria is as good as non-existent, since their position in relation to one 

 another does not change ; and this is due to the fact that the movement 

 is a common one in which they all take part. If of the wares on the 

 ship one bale moves only an inch away from the chest, this is for it a . 



