Magnetism

a force possessed by certain iron ores called lodestone. The lodestone was well known to the ancients. When a lodestone is brought in contact with a mixture of the fine particles of various materials, it will select and attract particles of iron and steel very noticeably. Nickel, cobalt, and a few others are attracted slightly. Bits of lead, copper, and wood are not attracted. If a bar of steel be brought into contact with the lodestone, especially if it be stroked from end to end, it acquires the properties of the lodestone itself, and will in turn attract particles of iron and steel. Such a bar is called a magnet. If placed on a piece of cork floating in water, or if suspended on a pivot so that it may revolve readily, it assumes a north and south direction, a property of which advantage is taken in the construction of the mariner's compass. The end of the magnet that turns north is called the north or positive pole; the opposite end is called the south or negative pole. The earth, itself, is a huge magnet. Its magnetic poles are in the Arctic and Antarctic zones, but do not coincide with the north and south geographical poles.

The lodestone is thought to have become magnetized by the earth. We observe that masses of iron which remain stationary for any length of time become magnetic. For this reason, tools lying idle in a workshop become magnetized. A steel rod held in a position parallel to the dipping needle becomes magnetized. When a magnet is heated to redness, it loses permanently its magnetism. Red hot iron is not attracted by a magnet. Large electric magnets are used for unloading cars of scrap iron. The pieces of old iron cling to a large magnet like iron filings to the toy magnet. One magnet of this sort is used to load and unload steel rails, two tons at a time, and to lift steel ingots out of a ship. A magnet of this sort, suspended from a derrick, is capable of handling kegs of nails, seven at a load.

See Compass; Electro-Magnet