Fig. 178.—Arrangement of molecules in a saturated magnet.
206. Magnetic Fields and Lines of Force.—The behavior of magnets is better understood after observing and studying the lines of force of a magnet. The earliest descriptions of these are by William Gilbert, the first Englishman to appreciate fully the value of making experimental observations. He wrote a book in 1600 called De Magnete in which he published his experiments and discoveries in magnetism. (See p. 217.)
Magnetic lines of force may be observed by placing a magnet upon the table, then laying upon it a sheet of paper and sprinkling over the latter fine iron filings. On gently tapping the paper, the filings arrange themselves along curved lines extending from one end of the magnet to the other. These are called the magnetic lines of force. (See Fig. 179.) The space about a magnet in which the magnetic lines are found is called the magnetic field. (See Fig. 180.)
Fig. 179.—Iron filings on paper over a bar magnet.
Many interesting things have been discovered concerning the lines of force. Some of the facts of magnetic action are given a simple explanation if we think of them as due to the magnetic lines of force. A summary of several discoveries concerning magnetic fields follows:
(A) Magnetic lines of force run side by side and do not cross one another. (See magnetic fields.)
(B) Magnetic lines of force are believed to form "closed curves" or to be continuous. The part outside of the magnet is a continuation of the part within the magnet. (See Fig. 180.)
