The electrical target usually employed in determining velocities of projectiles consists of a wooden frame on which is strung a copper wire so as to make a continuous circuit arranged in parallel vertical lines about one inch or one and one half inches apart.

It frequently happens that a projectile will pass through this target without breaking the circuit, either by squeezing between the wires or because, when last repaired, the target was short-circuited unnoticed, so that the cutting of the wires did not break the circuit. The repair of this target takes considerable time.


Besides these objections to this target, another and more serious one is the irregularity in the manner of breaking the circuit. It has been proved that times required for a flat headed and an ogival headed projectile to rupture the current are very different.

To remedy these defects a new and very ingenious target has been devised and used with great success at the United States Military Academy at West Point. The top of the target is a wooden strip, F, on the upper side of which are screwed strips of copper, A A, about 1/2 in. wide, and 1/8 in. thick. The connection between two adjoining strips is made by a copper cartridge, C, which is dropped in a hole in the frame bored to receive it. This cartridge is the one used in the Springfield rifle. Inside the cartridge is a spiral spring, S, which, acting on the bottom of the hole and the head of the cartridge, tends to make the latter spring up, and so break the circuit.

To the hook, H, which is attached to the cartridge, is suspended, by means of a string, the lead weight, W, thus drawing down the cartridge and making the circuit between A and A'. All the weights being suspended the current comes in through the post, P, passes along the copper strips and out of the corresponding post on the other end.

On firing the projectile cuts a string, and the spring at once causes the cartridge to spring up, thus breaking the circuit.

It is not possible for the projectile to squeeze between the strings and not break the current, for in so doing the cartridge is tipped slightly, which is sufficient, as it breaks the current on one side.

This target is used in connection with the Boulenge chronograph. Two targets are established at a known distance apart, say 50 ft., and the time required for the projectile to pass over this distance is determined by finding the difference in the time of cutting of the two targets, by finding the difference in the time of falling of the two rods, caused by the demagnetization of two electromagnets in the same circuit with the targets.

By means of a disjunctor both rods are dropped at the same time, the shorter one releasing a knife blade which makes a cut on the longer one. Now both rods are hung from the magnets again and the gun is fired.

The projectile passes through the first target, breaks the circuit, demagnetizes the magnet of the longer rod, and it begins to fall. On passing through the second target, the projectile causes the shorter rod to fall. This releases the knife blade, and a second cut is made. The time corresponding to the distance between these cuts is the time the longer rod was falling before the second rod began to fall or the time between the cutting of the two targets by the projectile.

The distance between the cuts is measured, and the time corresponding to it can easily be found. Then the velocity of the projectile is equal to 50/t.

To repair this target, strings are prepared in advance of suitable length and looped at both ends, so that by placing the hook of the cartridge in one loop and that of the weight in the other the repair is quickly made.

This target has been used on the West Point proving ground to determine velocities over distances of 100 ft. interval to distances of only 9 ft. interval, and has given most satisfactory results.

[Continued from SUPPLEMENT, No. 786, page 12566.]