Police whistle

A whistle is an instrument which produces sound from a stream of gas, most commonly air. It may be mouth-operated, or powered by air pressure, steam, or other means. Whistles vary in size from a small slide whistle or nose flute type to a large multi-piped church organ.

Whistles have been around since early humans first carved out a gourd or branch and found they could make sound with it. In prehistoric Egypt, small shells were used as whistles. Many present day wind instruments are inheritors of these early whistles. With the rise of more mechanical power, other forms of whistles have been developed.

One characteristic of a whistle is that it creates a pure, or nearly pure, tone. The conversion of flow energy to sound comes from an interaction between a solid material and a fluid stream. The forces in some whistles are sufficient to set the solid material in motion. Classic examples are tones that result in galloping power lines, or the Tacoma Narrows Bridge (galloping Gertie). Other examples are circular disks set into vibration.

Depending on the geometry, there are two basic types of whistles: those that generate sound through oscillations of fluid mass flow, and those that generate sound through oscillations of the force applied to the surrounding medium.

Joseph Hudson set up J Hudson & Co in Birmingham, UK in 1870. With his younger brother James, he designed the 'Acme City' brass whistle. This became the first referee whistle used at association football matches during the 1878–79 Football Association Cup match between Nottingham Forest and Sheffield. Prior to the introduction of the whistle, handkerchiefs were used by the umpires to signal to the players.

In 1883 he began experimenting with pea-whistle designs that could produce an intense sound that could grab attention from over a mile away. His invention was discovered by accident, when he accidentally dropped his violin and it shattered on the floor. Observing how the discordant sound of the breaking strings travelled (trill effect), Hudson had the idea to put a pea in the whistle. Prior to this, whistles were much quieter, and were only thought of as musical instruments or toys for children. After observing the problems that local police were having with effectively communicating with rattles, he realised that his whistle designs could be used as an effective aid to their work.

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