=The North Pole.=—The north pole is not only one of the ends of the axis round which the Earth turns but close to it is the _north magnetic pole_ as well. By _magnetic_ we mean that the Earth behaves like a steel bar that has been magnetized. A steel bar magnet like that shown in Fig. 85 is strongest at its ends. One end is _positively_ magnetized, and we call this end its _north pole_, and the other end is _negatively_ magnetized, and we call this end its _south pole_. Magnetic lines of force stream from the south pole through the steel bar and reaching the north pole they stream through the air to the south pole, as shown by the curved lines, thus forming a _magnetic circuit_, just as two wires joined together may form an electric circuit. If we place a compass needle near the steel bar magnet the needle will turn in the same direction as the magnetic lines of force are flowing, and it will, therefore, point to the north and to the south poles of the magnet. Now the Earth is a great magnet with a positive pole, which we call the north pole at one end of its axis, and a negative pole, which we call the south pole, at the other end of its axis, as shown in Fig. 86. [Illustration: FIG. 85.—LINES OF FORCE THROUGH AND AROUND A MAGNET.] [Illustration: 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. [Illustration: FIG. 87.—WATCH SPRING—NEEDLE FOR COMPASS.] [Illustration: 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. [Illustration: FIG. 89.—POCKET WATCH-CASE COMPASS.] [Illustration: FIG. 90.—DIAL OF MARINER’S COMPASS.]