and the need for this extra sphere disappears.

They consider three main objections to the motion of the Earth: that a falling body would be left behind by the Earth and thus fall far to the west of its point of release; that a cannonball fired to the west would similarly fly much further than one fired to the east; and that a cannonball fired vertically would also land far to the west. Salviati shows that these do not take account of the impetus of the cannon. He also points out that attempting