The Electric Current, or Conductivity, System.—In this submarine telegraph system the water, which is a fairly good conductor of electricity, is made to carry an ordinary battery current between the sending and the receiving stations.
FIG. 59. THE UNDERWATER “WIRELESS.”
Since the water conducts the current of electricity, it is easy to see why it is called a conductivity system. It is also called an underwater wireless system, but while it is wireless in the sense that there are no connecting wires between the two stations, you must not confuse it with the real wireless system, which uses electric waves, for in the former the energy decreases as the cube of the distance and in the latter only as the square of the distance.
The Parts of the Conductivity System.—There are three principal parts to this system, and these are (1) the sending apparatus; (2) the receiving apparatus, and (3) the submerged copper plates which conduct the current from the sender into the water and from the water into the receptor.
The sending apparatus consists of (a) a source of direct current, and the storage battery supplies this; (b) a reactance, or kick coil, as it is commonly called; (c) a rotating interruptor, and (d) an ordinary telegraph key.
The receiving apparatus is made up of (a) a telephone induction coil, and (b) a pair of head telephone receivers. All of this is shown in [Fig. 59].
One of the submerged copper plates is fixed to the bow of the submarine’s hull, and the other is secured to the stern, in order to get the plates as far apart as possible. These plates are connected to a throw-over switch, so that either the sender or the receptor can be connected to the plates as the operator wishes.
How the System Works.—The instruments of the sending apparatus are connected up as shown in [Fig. 59]. Now when a message is to be sent from one submarine to another, the operator sets the rotary interruptor, which is run by an electric motor, to spinning, and this makes and breaks the current several hundred times a minute as long as he holds the key down which closes the circuit.