Theremin Cello or Fingerboard Theremin
Invented in the late 1920's by Lev Termen, known as the Fingerboard Theremin or Theremin Cello, instead of strings, it has a flexible plastic film fingerboard which, when touched, produces a tone.
As long as the finger remains depressed, a tone is sustained. The volume is controlled by a lever on the player's right and the tone color is controlled by knobs, and the sound is amplified by an external amplifier. It was also used by the great Stokowski to reinforce his orchestra's bass section, it is said that the subsonic rumblings made some of the orchestra members complain of sickness.
The instrument was used throughout the 1930's by a number of musicians most notably Leopold Stowkowski who commissioned Termen to design and build a bass Theremin Cello which was later abandoned due to the side effects caused by subharmonic frequencies on the orchestra's string section. The Theremin Cello was another adaptation of Leon Termen, who was originally a cellist himself.
All images courtesy of the National Music Museum
University of South Dakota, Vermillion, SD.