Illustration of the Serb-US physicist Nikola Tesla (1856-1943) in a light bulb. Tesla developed the alternating current (a.c.) induction motor, and helped advance a.c. power generation and transmission. He also worked on high-frequency a.c. currents, inventing the Tesla Coil, a transformer in which the primary and secondary coils are in resonance. He used it to create electric sparks 40 metres long, and in 1899 lit 200 electric lamps without wires.