42. Dip or Inclination. If a piece of steel be carefully balanced upon a support, and then magnetized, it will be found that it will no longer balance. The north pole will dip or point downward. Fig. 33 shows what happens to a needle when it is held in different positions over a bar magnet. It simply takes the directions of the lines of force as they pass from the north to the south pole of the magnet. As the earth's lines of force pass in curves from the north to the south magnetic pole, you can see why the magnetic needle dips, unless its south pole is made heavier than its north. Magnetic needles are balanced after they are magnetized.
Fig. 34.
Fig. 34 shows a simple form of dipping needle. These are often used by geologists and miners. In the hands of the prospector, the miner's compass, or dipping needle, proves a serviceable guide to the discovery and location of magnetic iron ore. In this instrument the magnetic needle is carefully balanced upon a horizontal axis within a graduated circle, and in which the needle will be found to assume a position inclined to the horizon. This angle of deviation is called the inclination or dip, and varies in different latitudes, and even at different times in the same place.
43. The Earth's Inductive Influence. The earth's magnetism acts inductively upon pieces of steel or iron upon its surface. If a piece of steel or iron, like a stove poker, for example, be held in a north and south line with its north end dipping considerably, it will be in the best position for the magnetism of the earth to act upon it; that is, it will lie in the direction taken by the earth's lines of force. If the poker be struck two or three times with a hammer to shake up its molecules, we shall find, upon testing it, that it has become magnetized. By this method we can pound magnetism right out of the air with a hammer. If the magnetized poker be held level, in an east and west direction, it will no longer be acted upon to advantage by the inductive influence of the earth, and we can easily hammer the magnetism out of it again. (For experiments on magnets and magnetism see "Study," Part I.)
CHAPTER III.
HOW ELECTRICITY IS GENERATED BY THE VOLTAIC CELL.
Fig. 35.