=EXPERIMENT 14. To find whether the poles of a magnet can be reversed.=
_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.
(B) Keeping the part, C, in contact with the N pole of H M, and using the N pole of H M as a pivot, turn the needle end for end so that its head will be in contact with the S pole of H M.
(C) Pull the needle straight from H M, being careful not to slide it in either direction.
(D) Test the polarity of the ends with O C (Fig. 5), and save it for the next experiment.
=EXPERIMENT 16. To study the bar magnet with two N poles.=
_Apparatus._ The strange magnet just made (Exp. 15); iron filings; compass, O C (No. 18).
=38. Directions.= (A) Sprinkle filings over the whole length of the needle and then raise it (Fig. 8).
(B) Break the needle at its center, and test, with O C, the two new ends produced at that point. Remember that repulsion is the test for polarity.