Page:Popular Astronomy - Airy - 1881.djvu/118

104 second law of motion is, that the force of gravity draws it just as far from the place which it would have reached, if no gravity were acting, as the force of gravity would draw it in the same time from the position of rest. Suppose, for instance, that a body is thrown in the direction of AB, (Figure 31,)

with a speed which would have carried it from A to B in one second of time; and suppose I know from experiment that it would have dropped from A to C in one second of time; then the second law of motion is this: that at the end of one second of time the body will really be found at D, having, by the action of gravity, been pulled away from the place B, which it would have reached with the original direction and the original velocity, just as much as if pulled away from the state of rest.

The law may be illustrated by experiments in this manner: AB, Figure 32, is a board; CD, an arm moving upon it, turning on a hinge at C, and driven by a spring E; at the end D of the arm is a hollow, with its opening in the side of the arm large enough to contain a small ball, so that when the arm is driven by the spring E, the ball will be thrown