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Rh a current, and the ultimate result is a spark. Now, this spark implies heat, and is, in truth, nothing else than small particles of intensely heated matter of some kind. We have here, therefore, first of all, the conversion of electrical separation into a current of electricity, and, secondly, the conversion of this current into heat. In this case, however, the current lasts only a very small time; the discharge, as it is called, of a Leyden jar being probably accomplished in $1⁄24000$th of a second.

91. In other cases we have electrical currents which, although not so powerful as that produced by discharging a Leyden jar, yet last longer, and are, in fact, continuous instead of momentary.

We may see a similar difference in the case of visible energy. Thus we might, by means of gunpowder, send up in a moment an enormous mass of water; or we might, by means of a fountain, send up the same mass in the course of time, and in a very much quieter manner. We have the same sort of difference in electrical discharges, and having spoken of the rushing together of two opposite electricities by means of an explosion and a spark, let us now speak of the eminently quiet and effective voltaic current, in which we have a continuous coming together of the same two agents.

92. It is not our object here to give a complete description, either historical or scientific, of the voltaic