Danish silver pocket thermometer with Réaumur scale Circa 1815

Silver pocket thermometer
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An interesting and rare, early silver pocket thermometer after the design of Frederic Houriet made by Larpent & Jürgensen in Copenhagen, Denmark, circa 1815. Gilt brass movement with bimetallic curb, a rack and pinion transmission with coiled return spring and a micrometric adjustable lever mounted at the end of the rack acted upon by the curb. White enamel dial with a Réaumur scale indicating the Degrés du froid (cold degrees), Glace (ice) and Degrés du chaud (hot degrees), a blued steel hand. The case is polished. Dial signed.
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Diameter: 63 mm
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Signed: Larpent & Jürgensen Kiöbenhavn
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This type of pocket thermometer was first made by Fréderic Houriet followed by Urban Jürgensen and Abraham Louis Breguet. It was described by Houriet in an advertising leaflet, unfortunately undated.

The bimetallic thermometer device is extensively explained and illustrated by Urban Jürgensen in ‘Principes Généraux de l’Exacte Mesure du Temps par les Horloges’, Copenhagen, 1805, pp. 245-253, pl. XIX.
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The Réaumur temperature scale (°Ré or °R) is named after the French physicist René-Antoine Ferchault de Réaumur (1683-1757), who developed this scale in 1731 based on an alcohol thermometer. The freezing point of water is set at 0 °Ré, and the boiling point of water at normal atmospheric pressure is set at 80 °Ré.