In May 1888 George Westinghouse, head of the Westinghouse Electric Company in Pittsburgh, bought the patent rights to Tesla’s polyphase system of alternating-current dynamos, transformers, and motors. The transaction precipitated a titanic power struggle between Edison’s direct-current systems and the Tesla-Westinghouse alternating-current approach, which eventually won out.
Tesla soon established his own laboratory, where his inventive mind could be given free rein. He experimented with shadow graphs similar to those that later were to be used by Wilhelm Röntgen when he discovered X-rays in 1895. Tesla’s countless experiments included work on a carbon button lamp, on the power of electrical resonance, and on various types of lighting.
In order to allay fears of alternating currents, Tesla gave exhibitions in his laboratory in which he lit lamps by allowing electricity to flow through his body. He was often invited to lecture at home and abroad. The Tesla coil, which he invented in 1891, is widely used today in radio and television sets and other electronic equipment. That year also marked the date of Tesla’s U.S. citizenship.