WHISTLES WITHOUT SOUND
Policemen in most of the large French towns can summon help without being heard. They are supplied with .whistles whose notes are far too high-pitched for the human ear to detect. • The inaudible sound-waves are pickup by microphones skilfully camouflaged throughout the city, and an alarm is flashed to central police headquarters. A policeman who scs a burglar at woru, can summon reinforcements without alarming the suspect. Ho can, too, direct the sending of aid in Morse code by using the soundless whistle..
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Bibliographic details
Manawatu Times, Volume LIII, Issue 6733, 9 October 1928, Page 12
Word Count
86WHISTLES WITHOUT SOUND Manawatu Times, Volume LIII, Issue 6733, 9 October 1928, Page 12
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