Page:The Gradual Acceptance of the Copernican Theory of the Universe.djvu/136

 fall following that perpendicular line, it is absolutely certain that that stone would land upon the spot aimed at perpendicularly underneath. But if the earth is moved, it would be impossible for the stone to strike that spot.

This I prove first: because either the air moves at an unequal rate with the earth; or it moves equally rapidly. If not equally, then it is certain the stone could not land at that spot, since the earth's movement would outstrip the stone borne by the air. If equally rapidly, then again the stone could not land at that spot, since although the air was moving in itself at an equal speed, yet on that account it could not carry the stone thus rapidly with itself and carrying it downward falling by its own weight, for the stone tending by gravity towards the center resists the carrying of the air.

You will say: if the earth is moved in a circle, so are all its parts; wherefore that stone in falling not only moves in a circle by the carrying of the air, but also in a circle because of its own nature as being part of the earth and having the same motion with it.

Verily this answer is worthless. For although the stone is turned in a circle by its own nature like the earth, yet its own natural gravity impeded it so that it is borne along that much the less swiftly, unlike the air or the earth, both of which are in their natural places and which in consequence have no gravity as a stone falling from on high has.

Lastly; because although the stone is moved in the world by its own nature like the whole earth, yet it is not borne along as swiftly as the whole earth. For as one stone by its own weight falls from the heaven following its own direct motion straight to the center just as a part of the earth, so also the whole earth itself would fall; and yet it would not fall so swiftly as the whole earth, for although the stone would be borne along in its sphere like the whole earth just as a part of it, yet it would not be borne along as swiftly as the whole earth; and so, in whatever way it is said, the motion of the earth ought always to outstrip the stone and leave it a long distance behind. Thus a stone could never fall at the point selected or a point perpendicularly beneath it. This is false. Ergo.

Ninthly: If the earth is moved in a circular orbit, it ought to pass from the west through the meridian to the east; consequently the air ought to move by the same path. But if this were so, then if an archer shot toward the east, his arrow ought to fly much farther than if he shot toward the west. For when he shot toward the east, the arrow would fly with the natural movement of the air and would have that supporting it. But when he shot toward the west, he would have the motion of the 128