BALLISTA
, a military engine much used by the ancients for throwing stones, darts, and javelins; and somewhat resembling our cross-bows, but much larger and stronger. The word is Latin, signifying a cross-bow; but is derived from the Greek ballw, to shoot, or throw.
Vegetius informs us, that the ballista discharged darts with such violence and rapidity, that nothing could resist their force: and Athenæus adds, that Agistratus made one of little more than 2 feet in length, that shot darts 500 paces. Authors have often confounded the ballista with the catapulta, attributing to the one what belongs to the other. According to Vitruvius, the ballista was made after divers manners, though all were used to the same purpose: one sort was framed with levers and bars; another with pullies; some with a crane; and others again with a toothed wheel. Marcellinus describes the ballista thus; A round iron cylinder is fastened between two planks, from which reaches a hollow square beam placed cross-wise, fastened with cords, to which are added screws. At one end of this stands the engineer, who puts a wooden shaft, or arrow, with a large head, into the cavity of the beam; this done, two men bend the engine, by drawing some wheels; when the top of the head is drawn to the utmost end of the cords, the shaft is driven out of the ballista, &c.
The ballista is ranked by the ancients in the sling kind, and its structure and effect reduced to the principles of that instrument; whence it is called by Hero and others, funda, and fundibulus. Gunther calls it Balearica machina, as a sling peculiar to the Balearic islands.—Perrault, in his notes on Vitruvius, gives a new contrivance of a like engine for throwing bombs without powder.
Fig. 1, Plate v, represents the ballista used in sieges, according to Folard: where 2, 2, denote the base of the ballista; 3, 4, upright beams; 5, 6, transverse beams; 7, 7, the two capitals in the upper transverse beam, (the lower transverse beam has also two similar capitals, which cannot be seen in this transverse figure); 9, 9, two posts or supports for strengthening the transverse beams; 10, 10, two skains of cords fastened to the capitals; 11, 11, two arms inserted between the two strands, or parts of the skains; 12, a cord fastened to the two arms; 13, darts which are shot by the ballista; 14, 14, curves in the upright beams, and in the concavity of which cushions are fastened, in order to break the force of the arms, which strike against them with great force when the dart is discharged; 16, the arbor of the machine, in which a straight groove or canal is formed to receive the darts, in order to their being shot by the ballista; 17, the nut of the trigger; 18, the roll or windlass, about which the cord is wound; 19, a hook, by which the cord is drawn towards the centre, and the ballista cocked; 20, a stage or table on which the arbor is in part sustained.
Ballista, in Practical Geometry, the same as the geometrical cross, called also Jacob's Staff. See Cross-Staff.
