29. Laws of Attraction and Repulsion. From experiments 11 and 12 are derived these laws:
(1) Like poles repel each other; (2) Unlike poles attract each other; (3) Either pole attracts and is attracted by unmagnetized iron or steel.
The attraction between a magnet and a piece of iron or steel is mutual. Attraction, alone, simply indicates that at least one of the bodies is magnetized; repulsion proves that both are magnetized.
EXPERIMENT 13. To learn how to produce a desired pole at a given end of a piece of steel.
Apparatus. Same as in [Exp. 9].
30. Directions. (A) Magnetize a sewing-needle ([Exp. 9]) by rubbing it upon the N pole of H M from point to head. Float it and locate its N pole.
(B) Take another needle that has not been magnetized, and rub it on the same pole (N) from head to point. Locate its N pole.
(C) Magnetize another needle by rubbing it from point to head upon the S pole of H M; locate its N pole. Can you now determine, beforehand, how the poles of the needle magnet will be arranged?
31. Rule for Poles. The end of a piece of steel which last touches a N pole of a magnet, for example, becomes a S pole.
32. Our Compass (No. 18). While the floating magnetic needle described in [Exp. 10], and shown in [Fig. 4], does very well, it will be found more convenient to[13] use a compass whenever poles of pieces of steel are to be tested. [Fig. 5] shows merely the cover of the box which serves as a base for the magnetic needle furnished. We shall hereafter speak of this apparatus as our compass, O C. (See Apparatus Book, Chap. VII, for various forms of home-made magnetic needles and compasses.)