Visual signaling by means of the lamp has been found to be very important and efficient. Experience has shown that during the first hours of a battle, particularly in an advance, before it has been possible to establish the telephone systems, the lamp has furnished the most dependable means of communication both by day and night. Even in stationary or trench warfare in sectors with well organized systems of communication, the lamp is most serviceable in transmitting short messages such as calling for a barrage, reinforcements, etc., for which arbitrary signals are used. In fact, this method is more precise than the use of rockets and more rapid than the telephone in transmitting information covered by these arbitrary signals. For these reasons, all important telephone lines near the front are paralleled by the lamp system.
Description of the Lamps.—The signaling lamps are made in three sizes called the 14, 24 and 35 centimeter lamps. These dimensions indicate the diameter of the reflector. The 24 cm lamp consists of a portable searchlight, similar in principal to an automobile headlight, but equipped with a sighting or aiming tube on top, a hinged lid to cover the glass reflector, and a two-wire cable used to connect the batteries for operating the bulb. The battery comprises eight dry cells in series, carried in two leather pouches, each holding four cells. These pouches are attached to a leather belt supported by shoulder straps. The belt has also an additional pouch in which three extra lamp bulbs are carried. A brass push button which projects through this pouch is used as a key in completing the battery and lamp circuit to make signals of short and long flashes. Connection between the lamp and battery is completed by the two wire cable and the plug and socket connector. The complete apparatus, comprising the lamp and the belt and three spare light bulbs and eight dry batteries, is furnished in a wooden carrying case. The 14 cm lamp is similar to the 24 cm, but smaller, using a battery of four dry cells and being slightly different in the manner in which it is carried. The 14 cm lamps come three in a wooden case with extra batteries and lamp bulbs. The 35 cm lamp is a larger model of the 24 cm lamp, is not as readily portable and employs a storage battery. it is used only for permanent installations.
Method of Operation. The lamp and battery circuit is completed by means of the plug and socket connector. The lid covering the reflector is then opened and the operator sights through the tube to locate the station with which he is to communicate, and signals by means of the push button key. It is essential that the lamp be held rigidly and the sighting tube be continuously aimed exactly at the receiving station during signaling. A slight movement of the lamp makes the signals appear blurred or entirely invisible to the receiving station. A lamp station should always be located in the shade or protected from direct sun rays, which would otherwise produce a continuous glare from the reflector and make the electric light signals invisible. A lamp may be held in the hand while signaling or fastened to anything that will aid stability. In permanent and semi-permanent stations an arrangement for holding the lamp in a fixed position, directed at the receiving station, should be installed. In addition, a wooden tube tapering down in size toward the outer end and being 6 ft. to 9 ft. long and approximately the size of the lamp at the inner end, should be constructed and also permanently aligned on the receiving station. This reduces the diffusion of the rays of the lamp, and also minimizes the possibility of the signals being read where not intended.
Adjustments of Lamps.—The reflecting apparatus of a lamp is carefully adjusted before it is issued. However, it is possible that a slightly different adjustment will give better results when a new bulb is inserted. To focus the lamp the light is flashed on some dark background, such as wall a few yards away, and the screws supporting the parabolic mirror carefully turned until the light becomes concentrated in the smallest possible circle. The adjustment screws are then tightened, but they should never be set tight. If the receiving operator is having trouble in receiving signals, he will inform the sending station by sending a series of dots. The sending operator will then examine his apparatus to see if the lamp is properly directed at the receiving station, if the reflector is out of focus, or if the battery has become weak. The receiving operator indicates the manner in which he is receiving the signals by the method in which he sends the dots. If the signals become worse, the dots are made more rapidly. As the adjustment becomes better, the dots are made more slowly. When a good readable adjustment has been obtained, he will signal BR, meaning “go ahead.”
PRECAUTIONS IN LAMP SIGNALING.
Don’t leave the lamp cover open when not in use.
Don’t forget to open it when you start to transmit.
Don’t touch the mirror. If necessary, it should be cleaned by wiping with gauze or cotton or wiped with clean water.
Don’t pull the wire cable fastened to the bottom of the lamp when removing from the box.
Don’t return broken or burned-out globes to the pouch, but throw them away unless ordered to turn them in. Don’t use the lamp for illuminating purposes.