Page:Elementary Text-book of Physics (Anthony, 1897).djvu/273

 238. Fundamental Facts.—Masses of iron ore are sometimes found which possess the property of attracting pieces of iron and a few other substances. Such masses are called natural magnets or lodestones. A bar of steel may be so treated as to acquire similar properties. It is then called a magnet. Such a magnetized steel bar may be used as fundamental in the investigation of the properties of magnetism.

If pieces of iron or steel be brought near a steel magnet, they are attracted by it, and unless removed by an outside force they remain permanently in contact with it. While in contact with the magnet, the pieces of iron or steel also exhibit magnetic properties. The iron almost wholly loses these properties when removed from the magnet. The steel retains them and itself becomes a magnet. The reason for this difference is not fully known. It is usually said to be due to a coercive force in the steel. The attractive power of the original magnet for other iron or steel remains unimpaired by the formation of new magnets.

A body which is thus magnetized or which has its magnetic condition disturbed is said to be affected by magnetic induction.

In an ordinary bar magnet there are two small regions, near the ends of the bar, at which the attractive powers of the magnet