the different contact springs of the various bells make contact, this mode is not very satisfactory. If the bells are single stroke bells, they work very well in series; but, to get trembling bells to work in series, it is best to adopt the form of bell recommended by Mr. F. C. Allsop. He says: "Perhaps the best plan is to use the form of bell shown at [Fig. 82], which, as will be seen from the figure, governs its vibrations, not by breaking the circuit, but by shunting its coils. On the current flowing round the electro-magnet, the armature is attracted, and the spring makes contact with the lower screw.
There now exists a path of practically no resistance from end to end. The current is therefore diverted from the magnet coils, and passes by the armature and lower screw to the next bell, the armature falling back against the top screw, and repeating the previous operation so long as the circuit is closed. Thus, no matter how many bells there be in the series, the circuit is never broken. This form of bell, however, does not ring so energetically as the ordinary form, with a corresponding amount of battery power."
Fig. 82.
Fig. 83.
[Fig. 83] illustrates the mode in which a bell, at a long distance, must be coupled up to work with a local battery and relay. The relay is not shown separately, but is supposed to be enclosed in the bell case. Here, on pressing the push at the external left-hand corner, the battery current passes into the relay at the distant station, and out at the right-hand earth-plate E returning to the left-hand earth-plate E. In doing this, it throws in circuit (just as long as the push is held down) the right-hand local battery, so that the bell rings by the current sent by the local battery, the more delicate relay working by the current sent from the distant battery.