After the electronic oscillator was invented in 1915, revolutionizing the radio industry, the Russian inventor Léon Thérémin used this technology to develop the first fully functional electronic musical instrument; originally called the etherphone, it became widely known as the theremin.
Without touching the instrument, the player controlled pitch through relative proximity of the right hand to a vertical antenna, and volume through similar movements of the left hand in relation to a horizontal antenna. The instrument employed a heterodyne, or beat frequency system, and boasted a range of three to four octaves.
On the invitation of Lenin, Thérémin travelled throughout Russia, demonstrating his instrument, and toured Europe in 1927, causing excitement in Germany, France, and England. Later that year, Thérémin travelled to the U.S., where he remained until 1938.
In 1929 he sold his patent to the Radio Corporation of America (RCA), which made and sold 500 instruments. Leopold Stokowski collaborated on a fingerboard version, which he used with the Philadelphia Orchestra from 1929 to 1931. Thérémin performed with the New York Philharmonic and Cleveland Orchestra, and presented several coast-to-coast broadcasts. He returned to the USSR in 1938.
This according to The theremin in the emergence of electronic music by Albert Glinsky, a dissertation accepted by New York University in 1992 (RILM Abstracts 1992-424).
The theremin is 100 years old this month! Above and below, the inventor in action.
BONUS: A brief presentation of further historical and technical information.