Linesof Force

Lines of Force, in magnetism, are imaginary lines representing the direction and magnitude of the resultant force at any point in a magnetic field. If fine iron filings are sifted on a card held over a magnet they arrange themselves along these lines, which invariably form closed figures. The action of one magnet upon another is such that they appear to have a tension in the direction of their length and a pressure at right angles to it; hence they tend to shorten themselves, which occurs when two unlike poles are attracted and approach each other. Any combination of magnets and currents tends to arrange itself so that the lines of force due to aU are in the same direction and as short as possible. In the C.G.S. units 411 lines of force proceed from unit magnetic pole.