Fig. 84.
Fig. 85.
At [Fig. 84], we have illustrated the mode of connecting up a continuous ringing bell, with a wire return. Of course, if the distance is great, or a roadway, etc., intervene, an overhead line and an earth plate may replace the lines shown therein, or both lines may be buried. It is possible, by using a Morse key ([Fig. 65]) constructed so as to make contact in one direction when not pressed down, and in the other when pressed down, to signal from either end of a circuit, using only one line wire and one return. The mode of connecting up for this purpose is shown at [Fig. 85]. At each end we have a battery and bell, with a double contact Morse key as shown, the Morse key at each end being connected through the intervention of the line wire through the central stud. The batteries and bells at each
station are connected to earth plates, as shown. Suppose now we depress the Morse key at the right-hand station. Since by so doing, we lift the back end of the lever, we throw our own bell out of circuit, but make contact between our battery and the line wire. Therefore the current traverses the line wire, enters in the left-hand Morse key, and, since this is not depressed, can, and does, pass into the bell, which therefore rings, then descends to the left-hand earth-plate, returning along the ground to the battery from whence it started at the right-hand E. If, on the contrary, the left-hand Morse key be depressed, while the right-hand key is not being manipulated, the current traverses in the opposite direction, and the right-hand bell rings. Instead of Morse keys, double contact pushes (that is, pushes making contact in one direction when not pressed, and in the opposite when pressed) may advantageously be employed. This latter arrangement is shown at [Fig. 86].