Nikola Tesla invents the Tesla coil, 1891

Background. Tesla worked at a laboratory at 175 Grand Street in Manhattan from 1889 to 1892. Prior to 1891, he had explored resonant circuits, building on earlier work by inventors like Henry Rowland. The Tesla coil is defined as a resonant transformer circuit, often consisting of two or three coupled resonant electric circuits, functioning on principles different from standard AC power transformers.

Invention and Patent. Tesla patented his Tesla coil circuit on April 25, 1891. The specific configuration invented was the two-coil resonant transformer, consisting of a primary winding for current pulses and a secondary winding producing high voltage. This design became the standard for virtually all present Tesla coils, distinguishing it from earlier resonant circuits using Leyden jars.

Demonstration and Application. Tesla first publicly demonstrated the coil on May 20, 1891, in a lecture before the American Institute of Electrical Engineers at Columbia College, New York. Following the invention, he experimented with transmitting power by inductive and capacitive coupling using high AC voltages generated with the coil, laying groundwork for his later wireless power work.