Again push the apple around another quarter circle and June 21 is reached. This time you will find the north pole is turned toward the Sun and this time it gets the light and heat for six months, while the south pole is away from the Sun and takes its turn of six months of night and winter. To us, however, it is the beginning of summer. [Fig. 83] shows the position of the Earth to the Sun at this time.
Pull the apple one more quarter of the circle round the candle and you will have completed its orbit just as the Earth swings round the Sun in 365 days. The seasons are more clearly shown in [Fig. 84].
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].
Fig. 85.—Lines of Force through
and around a Magnet.
