He continued: ‘When, however, the electrical agency is confined to bodies, such as the metals, and which are found to oppose but small resistance to its progress, then this violent expansive or disruptive action is either greatly reduced or avoided altogether; the explosive form of action we term lightning vanishes, and becomes, as it were, transformed into a sort of continuous current action of a comparatively quiescent kind, which, if the metallic substance it traverses be of certain _known_ dimensions, will not be productive of any damage to the metal; if, however, it be of small capacity--as in the case of a small wire--it may become heated and fused; in this case the electrical agency, as before, is so resisted in its course as to admit of its taking on a greater or less degree of explosive and heating effect, as in the former case. It is to be here observed, that all kinds of matter oppose some resistance to the progress of what is termed the electrical discharge, but the resistance through capacious metallic bodies is comparatively so small as to admit of being neglected under ordinary circumstances; hence it is, that such bodies have been termed conductors of electricity, whilst bodies such as air, glass, &c., which are found to oppose very considerable resistance to electrical action, are placed at the opposite extremity of the scale, and termed non-conductors or insulators. The resistance of a metallic copper wire to an ordinary electrical discharge from a battery was found so small, that the shock traversed the wire at the rate of 576,000 miles in a second. The resistance, however, through a metallic line of conduction, small as it be, increases with the length, and diminishes with the area of the section of the conductor, or as the quantity of metal increases.’