Fig. 38
13. The Electric Bell and Buzzer ([Fig. 38]).—So common a thing as an electric bell really belongs to the present generation. Bells were either novelties or toys when I was your age. They cost then many times what they do now and then were poorly made. Nobody dared to trust them for front-door bells. It was necessary to have a card permanently posted over the push button saying, "If the bell does not ring, knock." In those days batteries were troublesome to care for, houses were not wired when built, and no one had learned the art of concealing the wires neatly.
Fig. 39
The buzzer is simply a bell minus gong and hammer. Those shown in [Fig. 38] ring well on a single dry cell. A cell costing twelve cents operated one for two years while it was used as a call bell from dining room to kitchen, the current required being .15 ampere.
Electric Bell
The connections are shown in the diagram ([Fig. 39]). Suppose the current to enter at the binding post a, pass around the magnets b and then to the post c. The armature d normally rests against the post c and the current finds its way along this to the post e and thence back to the battery. But as soon as the current passes, b becomes a magnet and pulls the armature d away from the post c, thus breaking the circuit, when b ceases to be a magnet and a spring pushes the armature d back against the post c to repeat the operation. The armature d carries a hammer which strikes the gong f. If the wire, which is usually connected with the binding post e, is connected with the post c, the "clatter" bell is changed to a "single-stroke" bell, and if the gong and hammer are removed the "bell" is changed to a "buzzer."