This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The following diagrams will indicate a few of the various methods that may be employed in connecting up electric bells for different purposes, A, B and C representing the push buttons ; D, the bells; E, the batteries, and G, the ground. The simplest possible connection is shown in Fig. 1, the bell
D, battery E, and push button A, are all connected in series. The operation of the bell is independent of the order in which the bell, battery, and push button are placed, so long as there is a complete circuit when the push button is pressed. One of the wires in this circuit may be done away with by completing the circuit through the ground, as shown in Fig. 2. Connecting a bell as shown in this diagram often results in quite a saving of wire. The proper connections for operating one tell from either of two push buttons, A or B, is shown in Fig. 3. Two bells, D, operated from a single push button, C, are connected as shown