Terpsitone

The terpsitone was an electronic musical instrument invented by Léon Theremin. It consisted of a platform fitted with antennas, through and around which a dancer would control the musical performance. By most accounts, the instrument was nearly impossible to play. 
Theremin only built three of these instruments. Only the last one, made by Theremin in 1978 for Lydia Kavina, still exists today.