CATHODIC protection is complementary to the physical protection of metals, since it is used in conditions where painting and similar methods are not practicable, or not wholly satisfactory; in the case of metals which are buried in damp ground or immersed in aqueous fluids. The underlying principle is that, if metal surfaces in need of protection can be made completely cathodic, no corrosion will occur. This is effected by the introduction of an artificial anode which sets up a flow of current, the circuit of which is completed by the aqueous medium acting as the electrolyte.