The Armature.—But magnetism can no more be seen than electricity flowing through a wire. If a piece of metal has magnetism it will attract a piece of iron or steel placed in close proximity, and thus we are permitted to see the action.
The lightning in the upper atmosphere burns the gases in its path. This enables us to see, not the current, but its action,—the result produced by its power.
The electric current has many peculiar manifestations, the causes of some of them being known and utilized. In the use of this medium for igniting the fuel gas, many of the phases of electrical phenomena are brought into play, and it is necessary, therefore, to know something of the fundamentals of the science to enable us to apply it.
Characteristics of Electricity.—When a current passes along a wire, it does not describe a straight path, but it moves around the conductor in the form of circles. The current is not confined wholly to the wire itself, but it extends out a certain distance from it at all points.
Magnetic Field.—Every part of a wire which is carrying a current of electricity has, surrounding it, a magnetic field, of the same character, and to all intents and purposes, of the same nature as the magnetic field at the ends of a magnet.
Elasticity.—This current has also something akin to elasticity. That is, it surges to and fro, particularly when a current is interrupted in the circuit. At the instant of breaking a current in an electric light circuit there is a momentary flash which is much brighter than the normal light, which is due to the regular flow of the current.
This is due to the surging movement, or the elastic tension, in the current. Advantage is taken of this characteristic, in making a spark. This spark is produced at the instant that the ends of the wires are separated.
The Make and Break System.—No spark is caused by putting the two ends together, or by making the connection, but only by breaking it, hence it is termed the make and break method of ignition.
When the connection is broken the current tries to leap across the gap, and in doing so develops such an intense heat that the spark follows. As a result of the high temperature it is necessary to use such a material where the gap is formed that it will not be burned. For this purpose platinum, and other metals are now employed.
Voltage.—This plays an important part in ignition. Voltage is that quality which gives pressure or intensity to a current. It is the driving force, just as a head of water gives pressure to a stream of water.