_The Catapult._--The “Tormentum” of the Romans was a generic name for military engines, and so named from the twisting of the hair, thongs, sinews, &c., of which the propelling mechanism was made. What were the exact materials used, and in what proportions, is entirely unknown, and probably the knowledge did not extend beyond a century or so after the fall of the empire. There can be no doubt but that the sinews of animals played an important part in the construction of the skein. The method of making the catapult was as follows, omitting unnecessary details. A quadrangular wooden frame of great strength was fitted near one end with the skein, which was made in the form of a circle and of very considerable thickness, the rubber tyre of a large motor-car wheel approximating both in size and shape. This was folded into two parallel straight lines and passed through holes in the frame on either side, where a simple mechanism grasped it which could revolve the ends, cogs preventing them from turning in any direction but that desired. Between the parallel parts of the skein the end of the arm was placed, and by twisting the ends of the skein the arm was made to press with considerable force against a horizontal beam supported by uprights at the two sides. The arm was provided with a hollow in the upper part for holding the stone. If now the arm were drawn back by means of levers, ropes, and pulleys, the distortion upon the skein was increased enormously, and if when loaded with a projectile the arm were released, it sprang back against the beam with great velocity and force, throwing the stone to a distance during the action. This propulsive force was considerably augmented in some machines by the addition of a sling to the end of the arm, which practically lengthened the arm and consequently hurled the projectile to a greater distance. Ancient writers assert that the range was sometimes as much as from seven hundred to eight hundred yards. [Illustration: FIG. 440.--Principle of the balista.]