A current of electricity running around a wire, rings the door bell. Then why doesn't it ring all the time? For the same reason that an electric lamp doesn't give light all the time. In both cases we connect and break the current of electricity. The carbon filament in the lamp runs into platinum wires in the neck. When you push in a button or turn a thumb key, the platinum wires are made to touch the copper wire that carries the electric current into the house. The current flows around the carbon filament completing the circuit, and we get a light. So, when you press the button of a door bell a bit of metal under the button presses on the wire that, all the time, carries the electric current to that point. The current instantly leaps along the rest of the wire to the bell, and rings it. In the case of the lamp the current comes from a distant power house on wires, under the streets, between the walls and through the tubing of the electric light fixtures. In the case of the door bell, each house has its own little power plant in the basement, or on a closet shelf. It is an electric battery made with chemicals in a jar. Any careful, clever boy can make such a battery, and explain to a school just how a door bell is made to ring.