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Galton whistle[′gȯl·tən ‚wis·əl]
an acoustic radiator of the jet type in the frequency range from 2-3 to 40-50 kilohertz.
The action of the Galton whistle is based on the excitation of vibrations in a hollow cylinder, or resonator, by a stream of air flowing from a ring-shaped slot and impinging upon the sharp edge of the cylinder. Periodic eddies develop at the sharp edge and excite vibrations in the resonator’s air volume. The radiation frequency of the whistle depends upon the depth of the resonator (adjustable with a micrometer screw) and the air pressure. The Galton whistle was the first ultrasonic source. It was proposed by the English scientist F. Galton in 1883.