Thermometer

By uniting two or more metals into a compound strip, which changes curvature as the temperature changes, the design of metallic thermometers was greatly simplified, allowing them to become both more compact and more sensitive. Those in the shape of pocket watches, such as this example from around 1775 and signed by Johann Holtzmann of Vienna, were probably never intended to be anything other than a rich man's toy.

The glass-covered case protects the working movement of a bimetallic strip which moves the pointer across the enamelled dial, which has the central portion removed so that the simplicity of the works can be seen. The dial is marked with two scales, Reaumur and Fahrenheit, and the hand indicates both at once. The watch 'handle' is decorative.

Clockmakers produced barometers, often as a sideline, as their wealthy clients were interested in expensive items which might have a novelty appeal, such as this early piece of miniaturisation.

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