_=56. Polarization; Pole Pieces.=_ The wire, I W (Fig. 12), was acted upon by induction (Exp. 24) and behaved like a magnet. Poles were produced in it, so we say that the wire was _polarized_. Pieces of iron, placed upon the poles of a magnet, are called _pole pieces_. It should be noted that the lower end of the wire has a pole _like_ the pole of H M, to which it is attached. =EXPERIMENTS 27-30. To study pole pieces.= _Apparatus for Experiments 27-30._ Horseshoe magnet, H M; soft iron wires; iron filings, I F. =57. Directions.= (A) Suspend two wires, each about an inch long (Fig. 13) from one pole of H M. Do their lower ends attract or repel each other? [Illustration: Fig. 13.] [Illustration: Fig. 14.] =EXPERIMENT 28.= =58. Directions.= (A) Place the two wires just used so that one shall cling to the N pole of H M, and the other to the S pole of H M (Fig. 14). (B) Bring the lower ends of the wires near each other. Do they attract or repel each other? =EXPERIMENT 29.= =59. Directions.= (A) Bend a 2-inch iron wire, as in Fig. 15, and place it upon the poles of H M. (B) See if its central part, marked X, will strongly attract filings. [Illustration: Fig. 15.] [Illustration: Fig. 16.] =EXPERIMENT 30.= =60. Directions.= (A) Bend the wire just used a little more, and place its ends upon _one_ pole of H M (Fig. 16). (B) See if the iron filings and small wires will cling to its central part. CHAPTER IV. THE MAGNETIC FIELD. =EXPERIMENT 31. To study the space around a magnet, in which pieces of iron become temporary magnets by induction.= _Apparatus._ A bar magnet, B M (No. 21); a compass (No. 18); a sheet of stiff paper about 1 ft. (30 cm.) square, with a center line, C L, drawn parallel to one of its sides (Fig. 16-1/2), and with another line, E W, drawn perpendicular to C L. (See Apparatus Book, Chap. VI., for various ways of making home-made permanent magnets.) =61. Directions.= (A) Lay the paper upon the table, and place the compass over the center of the line, C L, previously drawn. (B) Place the eye directly over the compass-needle, then turn the paper until the line is N and S; that is, until the line is parallel to the length of the needle. Pin the paper to the table to hold its center line N and S. (C) Place B M upon the paper, as shown (Fig. 16-1/2), its N pole to the north, and its center at the cross line, E W. [Illustration: Fig. 16-1/2.] (D) Slowly move the compass entirely around and near B M, and note the various positions taken by the needle. Note especially the way in which its N pole points. This is to get a general idea of the action of the needle.