The Electric Current
One has to make inquiries concerning the laws which can be applied to electricity in motion. Whenever electricity is in motion, the motion requires the existence of some cause; it is assumed to be the electrical force due to a potential gradient. Such differences of potential arise whenever electricity accumulates at some point, example on the coating of a Leyden jar. The electric current tends to equalize the potential so that the Leyden jar loses its charge, its potential falls, and when this has become equal to that of the earth the current ceases. It is exactly the same with a stream of water. For water to flow it is necessary to have two containers, one at a higher level than the other; the lower container may be the sea, or a low-lying reservoir.