ELECTRIC FURNACES.) The high temperature of the electric arc is used for welding and cutting refractory metals. The arc is usually struck between the parts to be welded or cut and an electrode of carbon, or of the same metal as the material to be welded. In "spot welding" the parts to be welded are clamped together between heavy copper electrodes, and a very large alternating current is passed between the electrodes for a fraction of a second, or longer if necessary.
There are many minor but useful applications of electricity; e.g., electrically driven or con trolled clocks, electric firing of mines, electrical methods for geo physical exploration, electrical methods of recording, measuring and automatically controlling temperatures, electrical transmis sion of pictures and hand writing by wire and wireless methods, electric bells and fire alarms.