EXPERIMENT 10. To find whether a freely-swinging bar magnet tends to point in any particular direction.
Apparatus. [Fig. 4]. A magnetized sewing-needle ([Exp. 9]); the flat cork, Ck (No. 2); a dish of water. (You can use a tumbler, but a larger dish is better.)
23. Note. An oily sewing-needle may be floated without the cork by carefully lowering it to the surface of the water. All magnets, pieces of iron and steel, knives, etc., should be removed from the table when trying such experiments. Why?
24. Directions. (A) Place the little bar magnet (the needle) upon the floating cork, turn it in various positions, and note the result.
25. North-seeking Poles; South-seeking Poles; Pointing Power. It should be noted that the point swings to the north, provided the needle is magnetized as directed in [Exp. 9]. This is called the north, or north-seeking pole. The N-seeking pole is sometimes called the marked pole. For convenience, we shall hereafter speak of the N-seeking pole as the N pole, and of the S-seeking pole as the S pole. We shall hereafter speak of the tendency which a bar magnet has to point N and S, as its pointing power. An unmagnetized needle has no pointing power.
26. The Magnetic Needle; The Compass. A small bar magnet, supported upon a pivot, or suspended so that it may freely turn, is called a magnetic needle. When balanced upon a pivot having under it a graduated circle marked N, E, S, W, etc., it is called a compass. These have been used for centuries. (See Apparatus Book for Home-made Magnetic Needles.)
EXPERIMENT 11. To study the action of magnets upon each other.