(E) Place the compass in the position marked 1, which is on E W, about 1 in. from the line, C L. Press the wooden support down firmly upon the paper to show, by the dent made in the paper by the pin-head, the exact place on the paper that is under the center of the compass-needle. Before removing the compass from this position, look down upon it again, and make a dot on the paper with a pencil directly under each end of the needle. Remove the compass, and draw a line through the dent and the two dots just made. This will show a plan of the exact position of the needle. (F) Repeat this for the various points marked 2, 4, 6 in. from C L, always marking on the plan the position of the N pole of the needle. Do the same with the other points marked on Fig. 16-1/2 by dots, and study the resulting diagram. _=62. Discussion; The Magnetic Field.=_ The compass-needle was decidedly affected all around B M (Fig. 17), showing that induction can take place in a considerable space around a magnet; this space is called the _magnetic field_ of the magnet. Let us consider _one_ position taken by the compass-needle in the field of B M (Fig. 17), as, for example, the one in which the needle has been made black. The S pole of the black needle is attracted by the N pole of B M, and is repelled by the S pole of B M. The N pole of the compass-needle is attracted by the S pole of B M, and is repelled by B M's N pole. The position which it takes, therefore, is due to the action of these 4 forces, together with its tendency to point N and S. [Illustration: Fig. 17.] Every magnet has a certain magnetic field, with its lines of force passing through the surrounding air in certain definite positions. As soon, however, as a piece of iron or another magnet is brought within the field, the original position of the lines of force is changed. This has to be considered in the construction of electrical machinery. =EXPERIMENT 32. To study the magnetic field of a bar magnet.= _Apparatus._ A sheet of stiff paper; iron filings, I F; bar magnet, B M (No. 21); a sifter for the filings (No. 24); (See Apparatus Book, §48, 49, 50, for home-made sifters.) =63. Directions.= (A) Place B M upon the table, and lay the paper over it. (B) With the sifter sprinkle some filings upon the paper directly over B M, then tap the paper gently, to assist the particles to take final positions. Study the results. _=64. Magnetic Figures; Lines of Magnetic Force.=_ The filings clearly indicated the extent and nature of the magnetic field of B M. You should notice how the filings radiate from the poles, and how they form curves from one pole to the other. They make upon the paper a _magnetic figure_. Each particle of the filings becomes a little magnet, by induction (Exp. 24), and takes a position which depends upon attractions and repulsions, as discussed in Exp. 31.