Ballistic

or Electro-ballistic Machine . Is a machine designed to determine by electricity the initial velocity of a projectile. The West Point ballistic machine, devised for use at the Military Academy by Col. Benton, of the ordnance department, and since adopted by that department, consists of a bed-plate of metal supporting an arc placed in a perpendicular position, and graduated. Suspended perpendicular to the plane of this arc are two pendulums, having a common axis of motion pa ing through the centre. Two electro-magnets are attached to the horizontal limb of the arc to hold up the pendulums when they are deflected through angles of 90°. There is also an apparatus which records the point at which the pendulums pa each other, when they fall by the breaking of the currents which excite the magnets, two targets being placed so as to support the wires in a position to be cut by the projectile. The velocity of the electric currents being considered instantaneous, and the lo of the power of the magnets simultaneous with the rupture of the currents, it follows that each pendulum begins to move at the instant that the projectile cuts the wire, and that the interval of time corresponds to the difference of the arcs described by the pendulums up to the time of meeting.