Fig. 86.—Lines of Force
around the Earth.
Like a bar magnet, magnetic lines of force stream all over the Earth’s surface from the north pole to the south pole, and a compass needle placed anywhere on the Earth will swing round until it is in the same direction as the lines of magnetic force.
Fig. 87.—Watch Spring—Needle for Compass.
Fig. 88.—Compass Complete.
How to Make a Simple Compass.—Take a piece of watch spring about 3 inches long and straighten it. Heat the middle red-hot and let it cool slowly, when the temper will be taken out of it at this point. Place a center punch in the middle of the spring and strike it a sharp blow with a hammer; this will make a little dent in it. Bend it as shown in [Fig. 87]. To magnetize the needle rub one end on the north pole and the other end on the south pole of a steel magnet. Stick a sewing needle into a large cork and lay the magnetized needle on it, when it will point north and south, as shown in [Fig. 88].
Boxing the Compass.—There are two kinds of compasses in general use, though both kinds use a magnetized needle. The first kind is the ordinary pocket compass, with either a pull-off cover or one of the watch-case pattern. In this kind of a compass the magnetic needle is fitted with a jeweled center which swings on a steel needle; the dial is fixed in the case and is marked with the cardinal points, that is with the chief points of a compass. [Fig. 89] shows a pocket watch-case compass.
Fig. 89.—Pocket Watch-case Compass.