Page:Popular Astronomy - Airy - 1881.djvu/119

Rh horizontally from the hollow at D ; at F is another chamber opening downwards, its lower opening being

stopped by a board G, which will be knocked away by a blow of the arm CD; then it is plain that if one ball be put in D and another in F, the very same movement which throws one ball forward causes the other ball to drop at the same instant; and if the second law of motion be true, one of them will fall down vertically to the floor at H at the same instant at which the other, which is projected forward reaches the floor at K. And this does really happen so; the two balls do reach the floor at the same instant. What it proves is this: that if a ball is thrown horizontally it falls from that horizontal line down to the ground just in the same period of time as a ball which dropped from a state of rest.

I have described this experiment as applicable only to a horizontal throw; but it is equally applicable to an inclined throw, if the floor upon which the balls fall be inclined exactly in the same degree,