"The Thereminvox or Theremin was the first electronic musical instrument. Invented in 1919 by Russian Lev Sergeivitch Termen (later anglicized to Léon Théremin), the Thereminvox was an offshoot of government-sponsored research into proximity sensors. "
I find that it is remarkable that a musical instrument invented in 1919 is played completely by hand gestures in the aiir without touching the instrument. The sound is sci-fi trekie outworldly and would have been considered magic in the the 19th century.
Almost a century later have a look at "With a Wave of the Hand, Improvising on Kinect"