By placing both coils, A, upon the bundle of soft iron wires, G,
connecting one of them with the terminals of the battery, as shown in
Fig. 12, and holding the terminals of the other coil in the moistened
thumb and fingers of the two hands, when the battery circuit is opened
and closed by touching one of the wires to the battery, and removing
it, a slight shock will be felt from the coil which is disconnected
from the battery. By placing a coarse file in the circuit and drawing
one of the terminals along the file the circuit will be rapidly
interrupted. This shock is due to the current induced in the detached
coil by the magnetism of the bundle of wires.
[Illustration: FIG. 11.--MAGNETO-ELECTRIC INDUCTION.]