The dynamo brought into service not only light and power but heat; and the electric furnace in turn gave rise to several great metallurgical and chemical industries. Elihu Thomson's process of welding by means of the arc furnace found wide and varied applications. The commercial production of aluminum is due to the electric furnace and dates from 1886. It was in that year that H. Y. Castner of New York and C. M. Hall of Pittsburgh both invented the methods of manufacture which gave to the world the new metal, malleable and ductile, exceedingly light, and capable of a thousand uses. Carborundum is another product of the electric furnace. It was the invention of Edward B. Acheson, a graduate of the Edison laboratories. Acheson, in 1891, was trying to make artificial diamonds and produced instead the more useful carborundum, as well as the Acheson graphite, which at once found its place in industry. Another valuable product of the electric furnace was the calcium carbide first produced in 1892 by Thomas L. Wilson of Spray, North Carolina. This calcium carbide is the basis of acetylene gas, a powerful illuminant, and it is widely used in metallurgy, for welding and other purposes. At the same time with these developments the value of the alternating current came to be recognized. The transformer, an instrument developed on foundations laid by Henry and Faraday, made it possible to transmit electrical energy over great distances with little loss of power. Alternating currents were transformed by means of this instrument at the source, and were again converted at the point of use to a lower and convenient potential for local distribution and consumption. The first extensive use of the alternating current was in arc lighting, where the higher potentials could be employed on series lamps. Perhaps the chief American inventor in the domain of the alternating current is Elihu Thomson, who began his useful career as Professor of Chemistry and Mechanics in the Central High School of Philadelphia. Another great protagonist of the alternating current was George Westinghouse, who was quite as much an improver and inventor as a manufacturer of machinery. Two other inventors, at least, should not be forgotten in this connection: Nicola Tesla and Charles S. Bradley. Both of them had worked for Edison.