While the electro-magnet is, therefore, the form[p. 19] of device which is almost wholly used, it is necessary, first, to understand the principles of the permanent magnet.
Magnetism.—The curious force exerted by a magnet is called magnetism, but its origin has never been explained. We know its manifestations only, and laws have been formulated to explain its various phases; how to make it more or less intense; how to make its pull more effective; the shape and form of the magnet and the material most useful in its construction.
Materials for Magnets.—Iron and steel are the best materials for magnets. Some metals are non-magnetic, this applying to iron if combined with manganese. Others, like sulphur, zinc, bismuth, antimony, gold, silver and copper, not only are non-magnetic, but they are actually repelled by magnetism. They are called the diamagnetics.
Non-magnetic Materials.—Any non-magnetic body in the path of a magnetic force does not screen or diminish its action, whereas a magnetic substance will
In Fig. [5] we show the simplest form of magnet, merely a bar of steel (A) with the magnetic lines of force passing from end to end. It will be understood that these lines extend out on all sides, and not only along two sides, as shown in the drawing. The object is to explain clearly how the lines run.
