231. Directions. (A) Stand the compass and D C near each other ([Fig. 66]). Attach one end of an insulated copper wire, C W, to the binding-post, C, which is on the carbon plate of the cell. Do not join the other end to the other binding-post, Zn, of the zinc plate.
(B) With the left hand hold C W above and near the compass-needle, and in the N and S line, so that it will extend over the entire length of the needle.
(C) Take the free end of C W in the right hand and touch binding-post, Zn, for an instant only, watching the needle. Repeat.
232. Current Detectors. We know that a magnet can act, by induction, through the air upon a piece of iron or upon another magnet. The deflection of the needle in this experiment shows that there must be a magnetic field around a wire carrying a current. This fact is of the greatest possible importance. The simple magnetic needle, when used as above, becomes a detector of electricity.
EXPERIMENT 102. To study the construction and use of a simple "key."