Different figures may
be produced by using the solenoids without the iron cores.
EXPERIMENT SHOWING THE CURRENT.
By removing the coil, A, from beneath the compass, E, and connecting
the ends of the transverse wire, a' a', with the battery Fig. 16, then
lifting the plates of the battery out of the solution and allowing the
needle to come to rest, it will be found upon inserting the plates of
the battery in the solution, very gradually, that the deflection of
the needle will increase with the increase of plate surface submitted
to the action of the battery fluid; and if, when the greatest
deflection is reached, the coils or solenoids are introduced into the
circuit, one after the other, it, will be found that each added coil
diminishes the current, as will be shown by the diminished deflection
of the needle.
[Illustration: FIG. 16.--EXPERIMENT SHOWING THE CURRENT.]
MICROPHONE AND TELEPHONE.
Take two small carbon rods, p p, if procurable, if not, use two
ordinary nails, and connect them up in the circuit of the battery; lay
them upon a thin box so that the rods or nails cross each other, as in
Fig. 17; insert the electromagnet in the circuit; move the coils out a
little beyond the ends of the cores, lay a thin iron plate over the
ends of the coils, then jar the box upon which the bars, p p, are
laid, or drop a pin upon it, or scratch it with a piece of paper, and
the sound will be heard by placing the ear against the iron plate
resting upon the coils of the magnet.
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