|The Theremin was invented in 1919 by a Russian called Léon Theremin. It is the only musical instrument that is played without any actual physical contact - the notes are literally 'plucked' out of the air.
By moving your hands near the vertical and horizontal antennas you change the pitch and volume of the note produced.
The sound produced is an eery, almost human-like tone. You may well have heard the sound of the Theremin as they were often used in the sound-tracks to old Sci-Fi films such as 'The Day The Earth Stood Still'.
The Theremin never became widely popular - to make the thing sound melodic and tuneful requires a very good ear and lots of practice.
However, there is still interest in the instrument, There are web-sites, discussion groups and also companies which still manufacture the instrument.
My model of Theremin is called an Etherwave Pro and is made by Bob Moog in the States.