An instrument for determining the velocity of projectiles. The original pendulum was of very massive construction, the arc through which it receded when impinged on by the projectile, taking into account their respective weights, afforded, with considerable calculation, a measure of the velocity of impact. Latterly the electro-ballistic pendulum, which by means of electric currents is made to register with very great accuracy the time occupied by the projectile in passing over a measured space, has superseded it, as being more accurate, less cumbrous, and less laborious in its accompanying calculations.