Fig. 1.—The Card of a Mariner's Compass, Showing the "Points."
In the center of the card is a conical socket poised on an upright pin fixed in the bottom of the bowl, so that the card hanging on the pin turns freely around its center. On shipboard, the compass is so placed that a black mark, called the lubber’s line, is fixed in a position parallel to the keel. The point on the compass-card which is directly against this line indicates the direction of the ship’s head.
Experiments with Magnetism
The phenomena of magnetism and its laws form a very important branch of the study of electricity, for they play an important part in the construction of almost all electrical apparatus.
Dynamos, motors, telegraphs, telephones, wireless apparatus, voltmeters, ammeters, and so on through a practically endless list, depend upon magnetism for their operation.
Artificial Magnets are those made from steel by the application of a lodestone or some other magnetizing force.
The principal forms are the Bar and Horseshoe, so called from their shape. The process of making such a magnet is called Magnetization.
Fig. 2.—A Bar Magnet
Small horseshoe and bar magnets can be purchased at toy-stores. They can be used to perform very interesting and instructive experiments.