English: Large Tesla coil on display at Griffith Observatory in Los Angeles, CA. The coil itself is 48 in. high, 36 in. diameter at base narrowing to 18 in. diameter at top, with a 12 in. ball capacitive electrode mounted on top. This well-known coil is one of the oldest entertainment Tesla coils still in use. It was originally one of a pair of identical coils built in 1910 by Earle Ovington a manufacturer of high voltage medical coils who was a friend of Nikola Tesla. They were first displayed at the December Electrical Show at Madison Square Garden, New York City. At the show they were billed as the "Million Volt Oscillator". Installed in the balcony, on every hour the lights in the hall would dim for a spectacular display of 10 foot sparks between the two coils. Ovington gave the coils to Dr. Frederick Finch Strong, an occultist and one of the most well known proponents of electrotherapy, who used them to treat illnesses in his patients. In 1937 Strong donated them to the Griffiths Museum of the city of Los Angeles. The museum didn't have room to display them both and sold one of the coils. The other one, above, has been in continuous use ever since. It was estimated by a General Electric engineer that it produces 1.2 million volts.