The secondary coil N, has the outlet wires O, P, which run to the spark plug Q on the engine.
The operation is as follows: When the switch G closes the circuit, the battery thus thrown in the primary coil magnetizes the core A, and the hammer H´ is attracted to the end of the core, thus breaking the circuit at the contact screw I. The result is that the core is immediately demagnetized, and the spring H draws the hammer back to be again attracted by the core which is again magnetized, so that the hammer on the vibrator arm H goes back and forth with great rapidity.
From the foregoing explanations it will be understood how the primary induces a high tension current in the secondary, and in order that the spark may occur at the right time, a timer for closing and opening the primary circuit must be provided. By this means an induced high tension current is caused to flow at the time the spark is needed in the cycle of the engine operation.
The Distributer.—The distributer is a timing device which controls both the primary and the secondary currents, and it also has reference to the revolving switch on the shaft of a magneto whereby the current is distributed to the various cylinders in regular order.
[Fig. 57] shows a form of distributer which will illustrate the construction. A is the shaft which is driven at one half the engine speed. It is usually run by suitable gearing direct from the shaft of the magneto.
Its outer end rests in a bearing plate B, of insulating material, which plate serves as the disk to hold the contact plates, 1, 2, 3, 4, to correspond with the four cylinders to which the current is to be distributed.
Wires 5, 6, 7, and 8, run to the respective spark plugs C from these contact plates. The projecting end of the shaft A carries thereon a contact finger D, which is designed to contact with the respective plates, and an insulating ring E is interposed between the shaft and finger so as to prevent short circuiting of the high tension current.
On the side of the finger is a hub F, integral therewith, and a wiper attached to a post bears against the hub so as to form continuous contact. A wire leads from the post to one terminal of the secondary coil.