It is to be remembered that electrolysis is caused by the leakage current from the track systems of electrical street railways; all other sources of stray current are accidental and, therefore, negligible. In general, it is against common sense to blame corrosion on electrolysis where the damage is done a half-mile or so from any of the street railway's track systems or power supply points, when the pipe system is cast-iron, jointed with cement. It is possible to imagine conditions under which electrolysis can occur at such distances from the affecting railway system, such as interlacing networks of castiron water-pipes and wrought-iron, welded gas-pipes. Due to the electrical principles involved, electrolysis would occur under these conditions much less often than these construction conditions are found.