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Natural Magnets. Artificial Magnets. Magnetic Field of Force.

It was known to the ancients that certain hard, black stones, an iron ore consisting of iron and oxygen found notably at Magnesia in Asia Minor, possessed the power of attracting small pieces of iron or steel. This almost magic attribute of the stone was early turned to account in navigation and secured for it the name of Lodestone (leading-stone) because of its remarkable property of pointing north and south when suspended by a thread. The name of magnet (magnes lapis) was also given to these stones.

Magnetism is the peculiar property occassionally possessed by certain bodies (more especially by iron and steel) whereby they attract or repel one another.

If a piece of hard iron or steel be rubbed with a lodestone it will be found to have also acquired the properties of the stone. If hung up by a thread it will point north and south, will attract light bits of iron and if dipped into iron filings will cause the latter to cling in two small tufts near the ends with few, if any, near the middle.

FIG. 1. Lodestone which has been Dipped in Filings to show Poles

This indicates that the attractive power of the magnet is concentrated in two opposite parts. These parts are called the Poles. The line joining the poles is the Magnetic Axis.

Artificial Magnets are those made from steel by the aid of a lodestone or some other magnetising force. The principal forms of artificial magnets are the Bar and Horseshoe, so called from their shape.

FIG. 2. Bar and Horseshoe Magnet.

If a magnet (either artificial or natural) is suspended by a thread so that it may swing freely, and a second magnet held in the hand is presented successively to the two poles of the first, it will be observed that one pole is attracted and swings toward the magnet held in the hand, but that the other is repelled and swings away.

FIG. 3. Lodestone suspended from thread so as to point North and South.

Furthermore, if the poles of the suspended magnet are marked so as to easily be identified it will be found that it is always the same pole that swings towards the north. There would therefore appear to be two kinds of magnetism or at least two kinds of magnetic poles. The end swinging toward the north is termed the "north seeking pole" and the opposite end called the "south seeking pole." In common parlance they are simply termed the North and South poles. It is usual to mark the North Pole with the letter N.

There is no known insulator of magnetism: it passes through everything. A magnetic substance is one which offers little resistance to the field of force.

Magnetism flows along certain lines called Lines of Magnetic Force. These lines always form closed paths or circuits. The region in the neighborhood of a magnet through which these lines pass is called the Field of Force and the path through which they flow is called the Magnetic Circuit.

FIG. 4. Lines of Force around a Bar Magnet.

The paths of the lines of force can be demonstrated by placing a piece of paper over a bar magnet and then sprinkling iron filings over the paper which should be jarred slightly in order that the filings may be drawn into the magnetic paths. The filings arrange themselves in curved lines, diverging from one pole of the magnet and meeting again at the opposite end. The lines of force are considered as extending outward from the North pole of the magnet, curving around through the air to the South pole and completing the circuit back through the magnet.

The phenomena of magnetism and its laws form a very important branch of the study of electricity, for they play a part in the construction and operation of almost all electrical apparatus.