Page:The aborigines of Australia.djvu/91

76 be communicated without any projectile force the instrument would move backwards. Now, as the force with which it is thrown is constantly diminishing, while the rotation continues, it must always arrive at a certain point where these opposite forces balance or equalize each other. At that moment the weapon would fall to the ground were it not for its flat surface and rotary motion; but in consequence of the centre of gravity being so placed that it will always present its broad surface to the air, it cannot descend perpendicularly, but slides down the inclined plane up which it has been thrown, in consequence of the whirling motion continuing after the projectile force has ceased; so that, if properly thrown, it will pass over the head of the thrower, and often to a considerable distance behind him. On the same principle, a hoop thrown from the hand with a spinning motion inwards will begin to return before it touches the ground, and also the curious, though not so familiar, instance of a ball fired from a musket, the barrel of which has been bent to the left, being carried at long distances considerably to the right of the object aimed at, in consequence of the rotation of the ball on its axis, caused by the right side of the barrel overcoming the projectile force, and thus carrying it across the right line of aim.

The boomerang may be illustrated in a room by merely cutting a piece of card into the same shape as the diagram, then holding it between the finger and thumb of the left hand at an inclination of about