We have selected this branch of experimental science because it is very popular. Useful and various objects for experiments are easily made.

First of all you must have a battery. Batteries are so cheap to buy, that we do not give any long description of the various forms in use, but will confine ourselves to one form, which is easily made at home. If you want a Grove's battery, or a Bunsen for powerful heating purposes, try and get one second-hand; and Leclauche's or a bi-chromate battery for ringing electric bells or for telephone purposes can be obtained very cheaply indeed. To thoroughly understand the working of an electric battery, it is better that you should make one. We will therefore give the method of making a Danielle's cell, that is easily and cheaply made at home; and in a similar way so can the Bunsen. We will therefore describe these two forms.

First, the Danielle. It is a constant battery of very tuple form, and for electropying and electroplating, purposes it is very useful; also for magnetic experiments. You know what we mean by the term "constant." It is a battery that keeps up a current of the same strength for a very long time. For this purpose we must have two different metals, two different liquids, and two different vessels to contain the liquids, and into which we can immerse the metals.

For the outer vessel take a jam-jar; a pint jar is a convenient size. Then obtain a thin sheet of copper long enough to coil round the inside of the jar, and as wide as the jar is deep. Then as the coil should slip inside the jar loosely, cut a strip of the copper about 7/8 inch wide along the end, leaving about ½ inch at the top, so that the strip may be turned back, forming a handle by which the copper cylinder can be lifted out, also for a metallic connection to which others may be made. Now get a porous cylinder about 1½or 2 inches across, for the inner cell. A substitute for this cell may be made of two or three layers of thick brown paper rolled round a ruler or thick cylinder of wood, and tied tightly round a large cork, for the lower end. Only in this case the cylinder will be hardly strong enough to support itself after a short time, so that the porous earthen cylinder will be best, and it will only cost a few pence. Fig. 140 shows the general form of the Danielle's cell. The metal for the porous cylinder must be of zinc, and may be in the form of a rod, or thin sheet zinc rolled. Both surfaces must be amalgamated. To do this in the case of a rod is easy. Immerse it for a short time in sulphuric acid and water till the surface becomes rough, which it will do in the course few minutes. Then take it out and rub on it some quicksilver. The surface will then be bright, wearing the lustre of the latter metal. A piece of flannel or tow, or even a soft cork, will do for rubbing on the quicksilver. To charge this cell, the outer one must have a strong solution of sulphate of copper, with a little sulphuric acid added; and the inner cell is to be charged with a solution made by adding ten measures of water to one measure of sulphuric acid. With three, four, or five of such cells you will get a fairly powerful battery. Make a wooden tray to contain them, and to join them into series. Let the copper of one cell be joined to the zinc of another. For other particulars refer to an elementary book on Electricity. If you have not studied electricity before, it will be the more needful for you to do so, for it is important that you should know exactly what you are doing.

Fig 14. - Daniell's Cell.

For the Bunsen battery the pots are much the same as for the Daniell. You must have an outer glazed vessel, and a porous inner vessel For the inner vessel you must get a block of graphite some-wh&b larger than the height of your porous jar. These you must buy; ask for"battery carbons," and you will be supplied with what you require. For the outer cell you want zinc cylinders. It is better to buy these than make them yourself. The best are made in rolled zinc, and are sold at so much per pound. Get fairly thick zincs. Then amalgamate them as directed for the zinc in the Daniell cell. You will also require binding-screws to fit both the carbons and the zincs. These grasp the plate with one screw, and the heads of the screws take the wires to carry the electrical effect to the various apparatus to which it is applied.

Bunsen's battery is made in different forms, but the pot form you can understand from Fig. 140. With six or eight cells you will be able to get powerful effects; even a small electric arc light.