GALVANIC BATTERY. —When a number of copper and zinc pairs, similar to the one already referred to, are put together, so that the copper plate of one cell is placed in conducting connection with tile zinc plate of the next, they constitute a galvanic bat tery. The term battery is sometimes also applied to a number of cells acting as one combination, in whatever way they may be connected. When the terminal copper and zinc, plates are connected, the current runs from each copper to each zinc plate without the liquids, and from each zinc to each copper plate within the liquids; and when the contact is broken, the zinc pole shows negative, and the copper pole positive, electricity. The galvanic battery acts thus in all respects as a compound galvanic pair. If the polar wires be connected with a tangent galvanometer, the deflection of the needle caused by the battery will be exactly the same as that effected by one of the cells; provided the * wire be thick, and a good conductor; but if the zinc end be connected with the ground, and the electric tension of the insulated copper pole be tested by a condenser and its tension is found to be as many times greater than the tension of the same pole of one cell examined in the same way, as them arc cells in the combination. Thus, if two cells be taken, the tension is doubled; if three, tripled; and so on. The electro motive force of IL battery/ is therefore proportional to the nwmber of cells, supposing, of course, that they are arranged consecutively.. Hence the electricity of a battery is better able to force its way through imperfect conductor's than that of the simple pair. When the interpolar communication is formed by a thick short wire, a single cell produces as powerful an effect on the magnetic needle as a battery; but if it be formed by a bad conductor, such as a long and. thin wire, or a liquid, the effect is very. different. The current of the pair is then nearly stopped, and its .influence on the needle small, while that of the battery continues .to flow comparatively unimpaired. When a battery is put
up in series,.it is said to have a tension arrangement; when put up so that several of the cells are grouped together, so as to act as one large cell, it is said to have a tension arrangement. Thus 20 cells are arranged for tension when joined in succession; but they may be disposed so its to act as one large cell 20 times as large, or as 10 cells twice as largo, or as 5 cells four times as large, and so on. The disposition or size of the cells is determined from the circuit.
Delferent Forms of the Galvanic Battery.—Volta's pae\consists of.a number of circular plates, each made up of a plate of copper and a plate of zinc soldered together, built up, the copper plates facing one way, and the zinc the other, each compound plate being separated by a circular piece of woolen cloth, moistened with a solution of common salt, or dilute sulphuric acid. In consequence of the great number of pairs, the electric ten sion of the poles of Volta's pile is considerable. One furnished with from 60 to 100 plates can charge an electroscope without the condensing plates. It is from this battery that the term " pile" is applied to the galvanic or voltaic battery. Volta used another form of battery. which he called a crown of cups. This consisted of a number'of cells arranged in a circle, so that the first and last were contiguous.
Zamboni's Dry Pile consists of several hundreds, and sometimes thousands, of disks of paper thinned on one side, and covered with hinoxide of manganese on the other, put together consecutively, as in Volta's pile, and placed under pressure in an insulating glass tube closed with brass ends, which serve as the poles. The electric tension of the poles of this arrangement is considerable, hut the sirength•of the current which passea when the poles are joined, is.next to pothin. The of the dry pile is in the construction of a very delicate electrometer, which is named after itr inventor, Bohenenberger's electrometer.