When a shot is fired the report acts upon the microphone and upon the relay in turn. Immediately a magnetic clutch, which is placed upon the motor drive of the projector, is released, and a brake arrests the movement of the projector mechanism. Thus, the passage of the film is stopped in the gate, so that the picture remains stationary upon the screen.
The screen itself consists of three separate sheets of specially prepared thick paper. The front sheet is coiled upon a horizontal roller which is mounted at the bottom. From this it is carried up and over a second horizontal roller at the top of the screen space, and then down again behind the front sheet, to be coiled upon a third horizontal roller, mounted above the first one. As the lower front roller can be moved or "fed" the paper is free to travel upwards over the top roller, and down again to be wound upon the third roller. Behind these two thicknesses of vertically travelling paper is mounted a third sheet. This is coiled upon a vertical roller at one side, passed across the back of the two front sheets, and coiled round a second vertical roller on the opposite side. It is kept very taut, and serves to hold the two sheets in front in close proximity. It is moved by hand at intervals.
Behind the screen are a number of arc electric lights, or other illuminants, out of the firing line. In this way the space behind the screen is brilliantly lighted. As the paper remains stationary while the projector is running, it follows that a shot must penetrate the three thicknesses of paper, and the puncture is shown by the light from behind coming through the shot-hole. Thus the marksman can see where his shot has struck.
When the projecting mechanism has been stopped, and the result has been read, the shot-hole has to be obliterated before the film is able to resume its forward movement. This is accomplished automatically as follows: The relay, while declutching the drive and applying the brake, also sets in motion a plunger in a dash-pot. The time of the vertical travel of this plunger is varied, but the mechanism remains stationary, and the shot-hole visible, during its movement. When it has reached the limit of its travel it establishes contacts which serve to set the screen mechanism in motion. On the lower horizontal roller carrying the supply of paper is a ratchet and pawl movement, actuated by a solenoid. When the plunger connected with the relay closes the screen mechanism circuit, the ratchet is moved, and the outer sheet of paper moves upward one-eighth of an inch, while its return forming the second sheet moves simultaneously and correspondingly downwards. The displacement of these two vertically moving sheets disturbs the line of holes caused by the shot, and through which the back light was shining, so that the spot of light is extinguished, and an opaque screen is presented. The inclusion of the third or back paper not only serves as a stiffener, but also acts as a means of lessening the possibility of a repeat, especially as it is moved gradually and at long intervals in a transverse direction. The movement of the travelling surfaces of paper is extremely small, approximately the diameter of a shot-hole, so that the consumption of paper is very low. When the first roller has been exhausted it is only necessary to replace it by the roller on which the paper has been rewound, and the paper can be used over again. The possibility of three old shot-holes coming once more into line without a shot being fired is so extremely remote as not to be worth consideration.
Soldiers Firing at the "Life Target."
The picture on the screen is thrown from the projector at right, and the picture is held stationary by the action of the report of the rifle caught by the microphone (marked X) upon the lantern mechanism.
Front View of the "Life Target," showing Screen Opening.