Tesla Coil high-frequency discharge demonstrator

Tesla coils transmit electrical energy between two magnetically coupled coils. They were used until the 1920s in wireless telegraphy—to send messages via Morse code, for example—and in more than hundred mad-scientist-style movies, such as Frankenstein in 1931. This tabletop Tesla coil was likely made for science classes, producing long, impressive sparks in the air and lighting a fluorescent tube held at a distance. Since a Tesla coil is really a radio transmitter without an antenna, Tesla is credited with helping invent the radio—he filed the first radio patent. And his legacy continues today, with his namesake battery-powered automobile and Tesla coils that are still made by hobbyists, demonstrating the beauty of machines that produce electricity.