The space surrounding a magnet over which the magnetic forces extend is known as the magnetic field. It is desirable to learn fully the direction and form taken by these magnetic lines of force, which we can easily do with the two bar magnets andiron filings nsed in the previous experiments. A sheet of thin, firm writing paper is glued to a wooden frame, made of strips of wood i" thick. The frame keeps the paper firmly stretched and free from wrinkles, Experiment 6.

Place the frame over a bar magnet, the latter just touching the under side of the paper. Sift the iron filings over paper, at the same time lightly tapping the frame with a small weight. The filings will be seen to arrange themselves in certain curves, thus producing a graphic illustration of the magnetic lines of force, or magnetic field surrounding the magnet. Experiment 7.

Place the second bar magnet parallel with the other, and about 1 1/2" from it, with the N pole of one magnet at the same end as the S pole of the other magnet. Again sprinkle the iron filings on the paper as before, and study the curves formed by the filings. Place the two N poles at the same end, and study the curves formed by the filings.

These experiments are important and should be made carefully and a sufficient number of times to firmly fix in the mind of the student, the action of the magnetic field under the several conditions of polarity above mentioned. A photographic record can be made by using a developing paper, arranging the filings by light from a ruby lantern and then exposing to white light and developing.

Another way is to use wax coated paper, upon which the filings are arranged, then heating the wax with a lamp held underneath at a proper distance to soften the wax sufficiently to allow the filings to embed themselves therein ; the wax quickly hardens upon withdrawing the lamp, firmly fixing the filings in position. Care must be taken not to ignite the wax or heat it to the extent that it will melt and drop into the lamp. Another way is to use gumed paper. When the filings are arranged, moisten the paper with spray from a vaporizer, then dry quickly over a stone.