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AÂ siren from J. Salleron, 24 Rue Pavee ( Ou Marais) Paris, Circa 1850-1880, in original case. In perfect working condition. ItÂ comprises a small air-chest at bottom with an oblique-perforated rotor and worm drive above. When air from a bellows is forced into the bottom, it blows out from a series of oblique 20 holes in the top of the air chest. These holes coincide with others in the rotor and cause it to rotate at high velocity, emiting and very loud wailing sound. By sliding the headgear to one side causes the worm on the rotor to engage with a pinion which in turn on the dials to revolve, indicating the speed of rotation.Â Case dimensions 20,5 x 12,5 x 8 cm Â Boerhaave Museum got one in there collection as well. See website page:Â http://www.museumboerhaave.nl/object/sirene-in-kist-v12117/