Editorial use only Nikola Tesla (1856-1943), Serb-US physicist. In 1884 Tesla emigrated to America. For a while he worked with Edison, but after advocating alternating current (AC) over Edison's preferred (and financially lucrative) direct current (DC), they parted. Tesla then developed the AC induction motor and improved AC generation. Alternating current, since it can be easily transformed up and down, is far easier to distribute than DC. Later Tesla invented an air-core transformer which created sparks 40 metres long. In 1899 he lit 200 electric lamps over 25 miles without wires. The SI unit of magnetic flux density is named after him.