Motor-car principles; the gasoline automobile

by Roger B. Whitman

When a piece of iron or steel is placed in contact with a magnet, the lines of force flow into it, and it becomes magnetized, throwing out lines of force and forming its own magnetic field, which is quite distinct from the magnetic field of the original magnet. If the piece is of iron, its lines of force and its field die away as soon as it is separated from the magnet, but a piece of steel once magnetized will retain its magnetism and, of course, its lines of force.

A wire of nonmagnetic metal, such as copper, for instance, will not have the slightest attraction for iron filings, but when an electric current is passed through it the filings will act as if the copper were a magnet, clinging to it as long as the current passes, and dropping as soon as the circuit is broken. As a matter of fact, an electric current sets up lines of magnetic force exactly similar to those of a permanent magnet, their number being in proportion to the strength of the current.

As has been stated, iron becomes magnetized when magnetic lines of force flow into it. If, therefore, a wire through which an electric current passes is wound around an iron rod, the lines of force set up by the current will pass into the rod and magnetize it, so that it sets up its own magnetic field. This magnetic field is created when the electric current starts flowing in the wire and dies out when the flow of the current is stopped, for then the lines of force due to the current die out, and the iron, which depends on them for its magnetism and which has not the ability to retain its lines of force, returns to its original nonmagnetic condition. An arrangement of this sort, consisting of a soft iron core, around which is wound a number of layers of insulated wire, forms an electro-magnet, and will produce a magnetic field whenever an electric current passes through the wire. The action is practically instantaneous, the magnetic field appearing and dying out on the making and breaking of the electric circuit.

A magnetic field may thus be produced by the action of an electric current, and an electric current in turn may be produced by the action of a magnetic field. To generate a current by this method it is only necessary to place a conductor forming a closed circuit in a magnetic field, and to change the strength of the field, making it stronger or weaker. For an example, a length of insulated wire may be wound on an iron bar, and the bar then touched with a magnet. As soon as the lines of force flow into the bar it becomes magnetized and sets up a magnetic field in which the lines of force follow the law and flow from one pole to the other through the air. The formation of this field is exceedingly rapid, but during the time that the field is forming and increasing to its full strength, an electric current will flow in the wire winding. When the field has reached its full strength, the flow of the current ceases. On separating the bar from the magnet it loses its magnetism, and the field set up by it dies away; or in other words, its strength undergoes another change, now growing weaker as the bar returns to a nonmagnetic condition. This dying out of the field generates another momentary flow of current in the wire, which moves in the direction opposite to the flow of the current generated while the strength of the field was increasing.

The current generated is called an induced current, and the method of producing it is called induction.

The intensity of the induced current in any given winding depends on the extent of the change in the strength of the field and upon the rapidity with which it occurs. A bar of iron is limited as to the strength to which it can be magnetized; or in other words, it can only set up a limited number of lines of force. Increasing the strength of the field from nothing to this point, or reducing its strength from this point to nothing, gives the greatest change in strength possible to obtain, and if this change occurs in the shortest possible time, then the current induced will be of the greatest intensity that can be obtained from a conductor of the size and length used.

For an understanding of the action of a magneto it is necessary to bear in mind the following points:

First. That a magnetic field is composed of lines of magnetic force that flow from one pole of the magnet to the other.

Second. That the lines of force will take the path that presents the least resistance.

Third. That an electric current will be generated, or induced, in a conductor placed in a magnetic field whenever the strength of the field changes.