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 This is the only musical instrument known to the writer that is played without being touched! The Theremin is named after Professor Theremin who, in 1928, amazed New York audiences when he demonstrated his ability "to obtain music from the ether".
The instrument has two rods protruding from its housing, each one forming one plate’ of a capacitor. The performers hands become the second  plates’ when held near the rods. The capacitive changes engendered in one rod controls the pitch of the tone, the other rod responding by varying the amplitude of the output. simple. experimental circuit is illustrated . The plate should be around 30cm. square. lt ls placed next to a radio receiver tuned to a fairly strong station around 900 kHz. The slug of the coil is then adjusted to obtain the most pleasing tone. When the hand is moved near the plate, the picth of the tone will change.