CHAPTER XXII.
ELECTROMAGNETISM.

383. Electromagnetism is the name given to magnetism that is developed by electricity. You have already seen that if a magnetic needle be placed in the magnetic field of a magnet, its N pole will point in the direction in which the lines of force pass on their way from the N to the S pole of the magnet. You have also seen that in the galvanoscope, etc., a coil of wire acts like a magnet when a current passes through it. Can we not, then, use the needle to study the lines of force about wires and coils?

Fig. 116.

Fig. 117.

EXPERIMENT 152. To study the lines of magnetic force about a straight wire carrying a current.

Apparatus. The compass, O C; key, K; dry cell, D C. Arrange as in [Fig. 116].