Nikola Tesla (1856-1943), Croatian physicist and electrical engineer. Tesla was educated at Graz and Prague, but in 1884 he emigrated to America. For a while he worked with Edison, but soon left to set up on his own. He developed the alternating current induction motor. He helped advance a.c. power generation and transmission. He then turned to high-frequency a.c. currents, inventing the Tesla Coil. This is an air-core 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 over 25 miles without wires. The SI unit of magnetic flux density is named after him.