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A323-26 · Aneroid
c.1880
Object Overview
This is a French Solid Mahogany Aneroid Barometer from around 1880, made by the Parisian firm Dubois & Casse. It is a large brass barometer set in its entirety into a luxurious, massive surround of solid mahogany. The instrument combines precise French mechanics with the solid, emphatically substantial style of presentation that was so valued on the British market.
The surround takes the form of a round drum, turned on a lathe from solid mahogany. Its profile is stepped. At the front is a flat face ring framed by a moulding. Behind it runs a deep concave cove that gives the case its bell-like silhouette. The profile is completed by a broad, stepped rear plinth. On the back is a brass plate with a hanging loop, stamped with the number 056. The rich figure of the mahogany and the deep, warm tone of its polished surface make the surround a decorative object in its own right, and its weight far exceeds what one would normally expect from a wall aneroid.
aneroid capsule tensioned on a C-spring
brass, glass, silvered brass, steel, wood
A brass barometer of a form popular at the time is mounted whole into the wooden surround. It is betrayed by the thin brass bezel on the front of the instrument. The bezel holds a flat mineral glass with a bevelled edge. At the centre of the glass sits a brass set hand with an arrow-shaped tip, operated by a brass knob on its arbor. With it, the owner marks the current reading in order to judge later whether the pressure has risen or fallen.
The dial is made of silvered brass. Its central field is occupied by a machine-made guilloché ornament: concentric bands of small lozenge-shaped cells, formed by the intersection of numerous circles, converge towards the centre, where they give way to fine radiating lines around the arbor. The pattern was produced on a rose engine fitted with an eccentric chuck. A fixed cutter engraved into the brass a series of circles of equal radius, the centre of each being shifted in turn around a small circle, while the workpiece was rotated by one division of the dividing plate between passes. The engine turning was done before silvering. The silver coating laid over it accentuates the pattern: each facet of the cut reflects light at its own angle, so the ornament shimmers at the slightest change of lighting. The central field is crossed by the main pointer of blued steel, with an arrow-shaped tip and a crescent-shaped counterpoise.
The barometric scale is laid out as an arc in the upper part of the dial and is calibrated in English inches of mercury over a range of 28–31 inches. Each inch is divided into twentieths, that is 0.05 inch. Along its outer edge the scale carries detailed weather indications in English: STORMY, MUCH RAIN, RAIN, CHANGE, FAIR, SET FAIR, VERY DRY. The English legends and the inch scale indicate that the instrument was made for export.
In the lower part of the dial, two semi-arc thermometers are arranged symmetrically, following the curve of the bezel. On the left is a spirit thermometer with Réaumur (−10…+40 °R) and CENTIGRADE (−10…+50 °C) scales. On the right is a mercury thermometer with a Fahrenheit scale (+20…+110 °F). The bulbs of the two thermometers almost touch at the lower edge of the dial, forming a kind of point of symmetry for the whole composition.
The instrument is driven by a conventional movement built around a corrugated brass aneroid capsule. Its upper diaphragm is held in tension by a steel C-spring mounted on a massive cast-iron bridge. The pillar screws on which the bridge is mounted have the square heads characteristic of Dubois & Casse. On open-dial barometers, where the movement is on display, these screws are given a decorative and protective bluing. Here the movement is hidden behind the dial, so the screws, like the bridge itself, are simply painted black. From the edge of the spring runs a brass main lever. Through a connecting link it is joined to the bell crank of the main arbor, which pivots on a trunnion mounting. From the vertical arm of the bell crank, a fusee chain runs to the pointer arbor. The chain is kept taut in the usual way by a flat spiral hairspring.
This barometer is a coherent instrument, carefully thought out in every detail: a precise French movement, an elegant engine-turned dial with two thermometers, and a monumental mahogany surround. Made for an English-speaking buyer, it shows well how French makers of the 1880s adapted their products to the tastes and habits of the British market, without compromising either the quality of the mechanism or the refinement of the finish.