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.
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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.
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.