Apparatus. [Fig. 6]. The horseshoe magnet, H M; a thin wire nail, W N, 2 in. (5 cm.) long; a piece of stiff paper, cut as shown, to hold W N; thread with which to suspend the paper; compass, O C (No. 18).
34. Directions. (A) Magnetize W N so that its point shall be a S pole. Test with O C to make sure that you are right.
(B) Swing W N in the paper ([Fig. 6]), then slowly bring the S pole of H M near its point. Note result.
(C) Quickly bring the S pole of H M near the point. Is W N still repelled? Has its S pole been reversed?
35. Discussion; Reversal of Poles. The poles of weak magnets may be easily reversed. This often occurs when the apparatus is mixed together. It is always best, before beginning an experiment, to remagnetize the pieces of steel which have already served as magnets. The same may be shown by magnetizing a needle, rubbing it first in one direction, and then in another upon the magnet, testing, in each case, the poles produced.
EXPERIMENT 15. To find whether we can make a magnet with two N poles.
Apparatus. The horseshoe magnet, H M; an unmagnetized sewing-needle; compass, O C (No. 18).
36. Note. You have already learned that the polarity of a weak magnet can be changed ([Exp. 14]). Can you think of any method by which two N poles can be made in one piece of steel?
37. Directions. (A) Place the needle upon H M, as in [Fig. 7].