The maestra stands still as a statue, hardly breathing, in trancelike concentration. Except for her hands. With a few subtle, quicksilver gestures that could be mistaken for sign language, she forms a melody, deftly sculpting the air into music. She controls invisible elements around her with an almost imperceptible flick of the wrist. Her audience sits in stunned silence, spellbound.

Clara Rockmore Clara Rockmore

This is the iconic image of the theremin: a supernatural aesthetic and sound. It is the only instrument that necessitates no physical contact in order to play it and remains the only space-controlled musical instrument. Over a century of existence, it has been adapted to sundry musical settings from classical to psychedelic rock, its ethereal, tremulous glissando finding a special niche in cult sci-fi and horror films (and who can forget the haunting theme song of Midsomer Murders).

Like the Jedi lightsaber, it has found its way, too, to the dark side. Anton S LaVey, founder of the Church of Satan, was reputedly a fine thereminist, initially using it as a device for ghost detection. No instrument has so entranced spectators – and been so misunderstood – since the glass...