Page:Electricity (1912) Kapp.djvu/117



Chapter II use has already been made of the term electric current. The term meant the transfer of a positive charge through a wire from a point where the potential is higher to one where the potential is lower. Observation shows that the quantity which can be transferred in unit time depends not only on the difference of potential, but also on the material and the cross section of the wire. A stout wire will transfer a bigger quantity in unit time than a thin wire, or, as we may also say, it is able to carry a bigger current. When it is a question of electricity in motion the conductor must have body, whilst as we have seen, with electricity at rest only the surface counts, or, to speak more correctly, only the capacity counts. But the capacity of a sphere in space, or of a Leyden jar, is quite independent of the thickness of the metal parts. A wooden sphere covered with the thinnest layer of gold-beater's skin will at the