Fig. 93.
Fig. 94.
If a combined generator and bell be fitted at each end of a line, it becomes possible to communicate both ways; one terminal of each instrument must be connected to the line, and the other terminal on each to earth. A combined generator and bell is shown at [Fig. 94]. These instruments are always ready for use, require no battery or press-buttons. The generator, [Fig. 92], will ring seven bells simultaneously, if required, so powerful is the current set up; and by using a switch any number of bells, placed in different positions, can be rung, by carrying a separate wire from the switch to the bell.
