Barometer

This barometer is constructed for use while travelling, and may well have been used for calculating the heights of mountains as it has a long scale which measures very low barometric pressure. There were great problems associated in constructing barometers which would travel without either air getting into the tube or mercury escaping from the cistern. This example was probably constructed in the Parisian workshop of Mossy, active between about 1780 and 1820.

A straight glass tube filled with mercury is enclosed in a tubular wooden case, the upper half of which rotates to reveal the tube and brass scale. The scale, which is unusually long, reads from 16 pouces 5 lignes to 20 pouces 9 lignes (a 'pouce' is roughly equal to an inch, and 12 'lignes' equal 1 'pouce'). It is signed 'Mossy AParis', and is dated 1785. A vernier divided into 12 parts runs on the right side of the scale.

Mossy had been supplying the great French chemist Lavoisier with barometers and thermometers since 1767, and his instruments were very highly thought of by other scientific practitioners.

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