The rendering of these couples is considerable; the small cells shown in Figs. 1 and 2 give about two amperes in short circuit; the large one gives 16 to 20 amperes. Two of these elements can replace a large Bunsen cell. They are remarkably constant. We may say that with a depolarizing surface double that of the zinc the battery will work without notable polarization, and almost until completely exhausted, even under the most unfavorable conditions. The transformation of the products, the change of the alkali into an alkaline salt of zinc, does not perceptibly vary the internal resistance. This great constancy is chiefly due to the progressive reduction of the depolarizing electrode to the state of very conductive metal, which augments its conductivity and its depolarizing power. The peroxide of manganese, which forms the base of an excellent battery for giving a small rendering, possesses at first better conductivity than oxide of copper, but this property is lost by reduction and transformation into lower oxides. It follows that the copper battery will give a very large quantity of electricity working through low resistances, while under these conditions manganese batteries are rapidly polarized. The energy contained in an oxide of copper and potash battery is very great, and far superior to that stored by an accumulator of the same weight, but the rendering is much less rapid. Potash may be employed in concentrated solution at 30, 40, 60 per cent.; solid potash can dissolve the oxide of zinc furnished by a weight of zinc more than one-third of its own weight. The quantity of oxide of copper to be employed exceeds by nearly one-quarter the weight of zinc which enters into action. These data allow of the reduction of the necessary substances to a very small relative weight. The oxide of copper batteries have given interesting results in their application to telephones. For theatrical purposes the same battery may be employed during the whole performance, instead of four or five batteries. Their durability is considerable; three elements will work continuously, night and day, Edison's carbon microphones for more than four months without sensible loss of power. Our elements will work for a hundred hours through low resistances, and can be worked at any moment, after several months, for example. It is only necessary to protect them by a cover from the action of the carbonic acid of the atmosphere. We prefer potash to soda for ordinary batteries, notwithstanding its price and its higher equivalent, because it does not produce, like soda, creeping salts. Various modes of regeneration render this battery very economical. The deposited copper absorbs oxygen pretty readily by simple exposure to damp air, and can be used again. An oxidizing flame produces the same result very rapidly.