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.

ELECTRO METALLURGY.

Dissolve an ounce of sulphate of copper in a half pint of water; add a few drops of sulphuric acid; connect with the zinc pole of the battery the object to be coppered.  To the wire connected with the carbon attach a small plate of copper.  Hang the object and the copper plate in the solution a short distance apart.  A deposit of copper will be quickly formed.

THE HEATING EFFECT OF THE CURRENT.

With a piece of very fine platinum wire (No. 36 or 40), placed in the circuit of the battery, the heating effect of the current may be shown.  A half inch of No. 36 platinum wire will serve for the experiment.  If the battery is in good condition it will heat from 1/8 to 1/4 inch of the wire red hot.  This is sufficient to light gas or an alcohol lamp, also to ignite powder or gun cotton.

A short piece of a watch hair spring, or a piece of very fine iron wire, if placed in the circuit will be made very hot.

DUPLICATION OF BATTERIES.

Should the experimenter desire to go more deeply into the effects of the current, he will need a more powerful battery.  The battery described has been made on a very simple plan, to enable the amateur to copy it without difficulty or great expense.  There is no mystery about the battery.  Any one can make it.  All that is required is a plate of zinc, two plates of carbon, some strips of wood and copper, and two common wood screws for each cell.  The tumblers may be had anywhere.