Fig. 12.—Repulsion between Similar Poles, Shown by Floating Needles.
The needles will then arrange themselves in different symmetrical groups, according to their number.
A bar magnet thrust among them will attract or repel them depending upon its polarity.
The upper ends of the needles should all have the same polarity, that is, all be either north or south poles.
Magnetism flows along certain lines called
Lines of Magnetic Force. These lines always form closed paths or circuits. The region in the neighborhood of a magnet through which these lines are passing is called the field of force, and the path through which they flow is called the
Magnetic Circuit. The paths of the lines of force can be easily demonstrated by placing a piece of paper over a bar magnet and then sprinkling iron filings over the paper, which should be jarred slightly in order that the filings may be drawn into the magnetic paths.
Fig. 13.—A Magnetic "Phantom," Showing the Field of Force about a Magnet.