The time between the two clicks can be short or long, to represent dots or dashes, which, together with spaces, represent letters. (For Telegraph Alphabet and complete directions for home-made keys, sounders, etc., see "Apparatus Book," Chapter XIV.)
Fig. 109.
Fig. 110.
Fig. 109 shows a form of home-made sounder. Fig. 110 shows one form of telegraph sounder. Over the poles of the horseshoe electromagnet is an armature fixed to a metal bar that can rock up and down. The instant the current passes through the coils the armature comes down until a stop-screw strikes firmly upon the metal frame, making the down click. As soon as the distant key is raised, the armature is firmly pulled back and another click is made. The two clicks differ in sound, and can be readily recognized by the operator.
111. Connections for Simple Line. Fig. 111 shows complete connections for a home-made telegraph line. The capital letters are used for the right side, R, and small letters for the left side, L. Gravity cells, B and b, are used. The sounders, S and s, and the keys, K and k, are shown by a top view. The broad black lines of S and s represent the armatures which are directly over the electromagnets. The keys have switches, E and e.
The two stations, R and L, may be in the same room, or in different houses. The return wire, R W, passes from the copper of b to the zinc of B. This is important, as the cells must help each other; that is, they are in series. The line wire, L W, passes from one station to the other, and the return may be through the wire, R W, or through the earth; but for short lines a wire is best.
Fig. 111.