On the other hand, were the moon's motion to be stopped for an instant, the moon would fall directly towards the earth, along the line AD.

The moon's actual orbit, resulting from these component forces, is AC.

Let AC represent the actual flight of the moon in one minute.

Then BC, which is obviously equal to AD, represents the distance which the moon virtually falls towards the earth in one minute.
Actual computation, based on measurements of the moon's orbit, showed this distance to be about fifteen feet.

Another computation showed that this is the distance that the moon would fall towards the earth under the influence of gravity, on the supposition that the force of gravity decreases inversely with the square of the distance; the basis of comparison being furnished by falling bodies at the surface of the earth.