Ballistic Pendulum.

Ballistic Pendulum. An instrument so named was invented by Benjamin Robins (q.v.), about 1742, to ascertain the speed of projectiles, and to prove the quality of gunpowder. It consists of a large block of wood suspended from a strong horizontal axis; and it is so solidly constructed as to bear a very heavy blow from a shot without injury. An excavated centre on one side of the block is filled with sand, packed in leather upon an iron frame; four bags form a filling or core. The core, forming the place of impact, is easily replaced after each firing. Straps of wrought iron suspend the block from the wrought-iron axis or shaft. The shaft-ends have knife-edges, which rest on V supports. The construction is such that a violent percussion makes only a very slight oscillatory movement in the block. A brass graduated limb measures the arc of vibration; and a brass slide is pushed forward by an index attached to a bar connected with the suspension straps. Another form of instrument for similar purposes is described under EPROUETTE. For ballistics, the science of missiles, see GUNNERY, and PROJECTILE.