These parts of the balista are the same in their action and mechanism as those of the catapult. FIG. 14 (OPPOSITE PAGE).--THE MECHANISM OF THE STOCK OF AN ARROW-THROWING BALISTA. A. Side view of the stock, with the arrow in the sliding trough before the bow-string is stretched. B. Surface view of the stock, with the arrow in the sliding trough before the bow-string is stretched. C. Section of the fore-end of the stock, and of the trough which slides in and along it. [Page 23] [Illustration: FIG. 14.--THE MECHANISM OF THE STOCK OF AN ARROW-THROWING BALISTA.] D. Surface view of the trough, with the trigger and catch for the bow-string. E. Side view, showing the keel (F) which slides along the slot cut in the surface of the stock as the trough is drawn back by the windlass. G. Enlarged view of the solid end of the trough. This sketch shows the catch for the bow-string, the trigger which sets it free, the ratchets which engage the cogs on the sides of the stock, and the slot cut in the stock for the dove-tailed keel of the trough to travel in. * * * * * Balistas were constructed of different sizes for the various purposes of siege and field warfare. The smallest of these engines was not much larger than a heavy crossbow, though it more than equalled the latter in power and range. The small balistas were chiefly used for shooting through loopholes and from battlemented walls at an enemy assaulting with scaling ladders and movable towers. The largest had arms of 3 ft. to 4 ft. in length, and skeins of twisted sinew of 6 in. to 8 in. in diameter. Judging from models I have made and carefully experimented with; it is certain that the more powerful balistas of the ancients could cast arrows, or rather feathered javelins, of from 5 to 6 lbs. weight, to a range of from 450 to 500 yards. [Page 24] [Illustration: FIG. 15.--BALISTA FOR THROWING STONE BALLS. Approximate scale: ½ in. = 1 foot. This engine is here shown with its bow-string only slightly drawn along its stock by the windlass.] It will be seen that this engine is almost identical in construction with the one last described. (Fig. 13, p. 21.) The difference is that it propelled a stone ball instead of a large arrow. The ball was driven along a square wooden trough, one-third of the diameter of the ball being enclosed by the sides of the trough so as to keep the missile in a true direction after the bow-string was released. The bow-string was in the form of a broad band, with an enlargement at its centre against which the ball rested. The description given of the mechanism and management of the engine for throwing arrows can be applied to the construction and manipulation of this form of balista, which was also made of large and small dimensions. [Page 25]