These experiments were first performed by Oersted, in 1819, and show that the region around a wire carrying a current of electricity has magnetic properties.
Fig. 77.—If a Loop of Wire is formed about a Compass Needle, the Deflection will be greater.
Another interesting experiment showing the magnetic effect of a current of electricity when passing through a wire may be performed by connecting a heavy copper wire to two or three bichromate-of-potash cells. Dip the wire into a pile of fine iron filings and a thick cluster of them will adhere to the wire as in Figure 78.
As soon as the circuit is broken so that the current of electricity ceases flowing, the filings will fall off, showing that the magnetic effect ceases with the current.
Fig. 78.—Iron Filings clustered on a Wire carrying a Current of Electricity.
These three simple experiments have shown that if a current of electricity is passed through a copper wire, the wire will deflect a compass needle, attract to itself iron filings, etc., as long as the current continues to flow. As soon as the current is shut off, the magnetic effect is destroyed.
The region in the neighborhood of a wire carrying a current is a field of force through which lines of magnetism are flowing in exactly the same way that they do in the neighborhood of a bar or horseshoe magnet.
