The leading authority on both man and machine is Albert Glinsky. He supported the Bolsheviks in 1917 and after the Revolution was in Leningrad working on surveillance equipment and pioneering an early form of television. The instrument that bears his name was developed in 1920 while he was experimenting with radio apparatus to measure the dielectric constant of gasses. This seems as improbable as Adolphe Sax stumbling across the saxophone whilst plumbing in a U-bend, but no less sensational is the invention itself. It resembles no more than a plain box of coils and wires with a couple of aerials protruding.
Operation is quite simple, but fiendishly difficult to master.
The theremin allows the natural body capacitance of the hands to control electrical fields in the air between the antennae. Astonishingly, the theremin is unique as the only musical instrument played with no actual physical contact. With one hand controlling the pitch, and the other the volume, the chaotic whines and groans can be modulated to produce discrete musical pitches. Played proficiently, the sound is not unlike the human voice, a kind of ghost in the machine. Imagine listening to the Star Trek theme on shortwave radio.