Luckily, he has books for his back-up.
Popular Electronics, April 1955.
The theremin is an early electronic musical instrument named after its Russian inventor, Professor Léon Theremin, who patented the device in 1928. The controlling section usually consists of two metal antennas which sense the position of the player’s hands and control oscillators for frequency with one hand, and amplitude (volume) with the other, so it can be played without being touched. The electric signals from the theremin are amplified and sent to a loudspeaker.