Chronoscope

An instrument for measuring minute intervals of time. The term is specially applied by military men to instruments for obtaining initial velocities. The gun-pendulum and ballistic-pendulum were formerly used for this purpose, but are now nearly obsolete. All modern chronoscopes use electricity as a transmitting agent. The general method of applying it is to have the current-bearing wires pa through two targets placed in the path of the projectile. These wires are cut by the projectile, and the interval between the succe ive ruptures is recorded by a delicate time-keeper. Knowing the distance between the targets, the velocity is obtained by dividing this space, expre ed in feet, by the number of seconds in the interval. Chronoscopes differ in the kind of time-keeper employed. One of the largest cla es of chronoscopes use the pendulum. The electro-ballistic machine of Col. Benton (U. S. Ordnance Department) may be taken as a type of this cla . It consists of two pendulums having equal times of vibration suspended from the same horizontal axis. When the pendulums are deflected, one to the right the other to the left, through angles of 90°, pieces of soft iron attached to them come in contact with electro-magnets, which serve to hold them up. Each of these magnets is excited by a current pa ing through one of the targets. When the targets are ruptured the pendulums fall, and in pa ing each other record the point of meeting by operating a delicate bent lever attached to one of them, which leaves a dot of ink on the arc in front of which the pendulums vibrate. The interval of time between the rupture of the two targets is obtained from a table of arcs and corresponding times. Col. Benton has also invented an instrument called velocimeter , in which he uses threads instead of electro-magnets to hold up the pendulums. The threads pa through the targets, and when they are cut the pendulums fall as before. This method has found considerable favor where great accuracy is not required.