The Colored Light System.—In this system incandescent electric lights of high candle power are placed back of bull’s-eyes, or lenses, made of colored glass, and these lights can be switched on and off and so form combinations that spell out words just as the colored flags do. This system is very much used for short range signaling at night.
The Searchlight System.—A searchlight, that is an electric arc light set in front of a silvered reflector, can be seen for long distances, and so it, too, is largely used for night signaling.
The searchlight, which can be turned in any direction, has a movable shutter, or metal disk in front of it, fixed to a handle, and when this is worked up and down like a telegraph key, the shutter cuts the light off and lets it shine forth accordingly.
By working the key, and hence the shutter, the light is broken up into dots and dashes of the regular Morse telegraph alphabet, and these short and long flashes are read by the operator on the other boat.
The Wireless Telegraph System.—The wireless telegraph has all the other systems of signaling, when the submarine is afloat, beaten by miles.
Among its advantages are (1) it can be used in the daytime as well as at night; (2) the electric waves it sends out cannot be seen and this makes it harder for an enemy ship to locate the boat it is on, and (3) its signaling range is not cut off by the curvature of the earth.
The Parts of a Wireless System.—There are three chief parts to every wireless telegraph system, and these are (1) the sending apparatus, or transmitter, as it is called; (2) the receiving apparatus, or receptor, as some “high-brow” has named it; and (3) the aerial wire, which is used for both sending and receiving.
FIG. 56. A, THE TRANSMITTER READY TO SEND. B, THE RECEIVER READY TO LISTEN IN.