Barometers Realm

The pediment is shaped as a flat cornice with a moulded overhang: the rectangular top shelf projects slightly over the rest of the case and has gently rounded corners; below it is a horizontal frieze, tapering down and blending smoothly into the vertical backboard. The wooden panel that serves as the support for the mercury tube is crafted from a single piece of solid wood. At both the top and bottom, shallow cutouts on either side emphasize the verticality of the composition—these cutouts serve no practical function, but contribute to the visual rhythm and balance of the design. The vertical board continues uninterrupted down to the glazed cistern compartment. The mercury cistern, connected to a short offset in the siphon tube, is housed in a separate rectangular box with a transparent front panel. The box is made from the same wood as the rest of the case, with precisely fitted framing. The front panel is a flat pane of mineral glass.

The barometer scale is mounted in the upper third of the case. It consists of a printed paper register plate, protected by flat glass held in place at the edges with thin brass strips. The register begins with the following inscription: “Une indication barométrique n’a que peu de signification si elle n’est comparée à celles qui l’ont précédée,” which translates as “A barometric reading has little meaning unless compared to those that preceded it.”

The barometric scale, graduated in millimetres of mercury, has an unusual feature: none of the values are rounded, as in traditional designs. Instead of the standard 730–780 mm range marked at 10 mm intervals, this scale is marked at: 729, 738, 747, 756, 765, 774, 783—each step separated by exactly 9 mm. Every value is paired with a typical French weather term, following a standard meteorological indication layout.

The central reference point is set at 756 mmHg, labelled Variable. The scale was clearly centered on this value, with symmetrical markings increasing and decreasing by 9 mm. This is notably lower than the conventional 760 mmHg Paris standard and more accurately reflects local atmospheric conditions.

The average atmospheric pressure in the Wallonia region (the French-speaking southern part of Belgium) ranges from 757 to 759 mmHg, with lowland areas (Mons, Namur, Liège) averaging around 758–759 mmHg, while the Ardennes plateau (Saint-Hubert, Bastogne, Rochefort), located at higher elevations (400–600 m above sea level), averages 755–757 mmHg.

The barometric scale on the register plate is slightly offset to the left, which in turn places the barometric tube itself slightly left of center on the wooden panel—an unusual and distinctive feature.

At the bottom of the register plate, it states that the barometer was invented by Torricelli in 1643; just below that appears the name of Ducenne, the maker or retailer.

This instrument stands as a refined example of provincial craftsmanship, combining scientific utility with understated elegance. Its asymmetric layout, localized pressure calibration, and the rare signature of J.J. Ducenne make it not only a functional barometer but also a historically valuable artifact rooted in the meteorological and artisanal heritage of 19th-century Wallonia.