A '''''' was realised by using a sensitive valve, which required little force to operate, to modulate the flow of a stream of
compressed air. The basic principle of the valves used in these devices was to pass the stream of compressed air through two partially overlapping combs. The sound vibrations to be amplified were applied to one of the combs, causing it to move laterally in relation to the other comb, varying the degree of overlap and so altering the flow of compressed air in sympathy with the sound vibrations. It was used by
Gaumont for the presentation of some of their early
sound films. Other compressed-air gramophones included the
Elgéphone. ==References==