The breaking of the circuit deënergizes the core, and the spring again draws the lever back to its normal position, ready for the next completion of the circuit by the timing device.
Such an arrangement is as simple as the spark plug usually employed in the use of the high tension system, although it is more expensive than the plug.
IGNITION. HIGH TENSION
This system is used to the largest extent, so that we ought to have a full explanation of the devices which are required to do the work. While magnetos are used with the low tension system, for the reasons stated, they are especially necessary with the Jump Spark method.
Magnetos.—The most important element in this system is the magneto, so we shall try and make the subject as explicit as possible. As stated, a magneto is a special type of dynamo which will now be explained. For this purpose it will be necessary to show the elementary operation of an alternating current dynamo.
Alternating Current.—In [Fig. 42] A is a bar of soft iron, around which is a coil of wire B, the wire being insulated, so that it will not touch the bar. There is no magnetism in this bar, and this simple form of structure is shown, merely to represent what is called the field of a dynamo.
The object of the coil of wire is to make a magnet of the bar, for the moment a current is sent over the wire, a magnet is formed, and the magnetism leaves the bar the moment the current ceases to flow. If this bar should be of hard steel it would retain the magnetism.