Barometers Realm

Before us is a compact Holometallic Barometer by Tremeschini, dating to circa 1860, housed in a round, barrel-shaped case made of solid-formed brass with softly flowing profile transitions. The case is fitted with a suspended brass ring, allowing for stationary wall mounting. On the front, the barometer is enclosed by a slender brass bezel that neatly retains a flat mineral glass, lending the instrument an elegant and restrained appearance.

The dial is made of cardboard mounted on a zinc plate—a constructional solution typical of the period, ensuring dimensional stability under changing humidity conditions. Executed in a restrained monochrome palette, it carries a concentric barometric scale: the outer ring is graduated in centimetres of mercury, while the inner ring is calibrated in Paris inches of mercury. The scale is supplemented with standard textual weather indications in the German language. The typography is distinguished by elongated, expressive letterforms with carefully rendered diacritical marks; umlauts and ligatures are executed consistently and with precision, characteristic of high-quality printing intended for the German-speaking market. Variations in lettering—alternating between heavy, fully blackened terms and visually lighter hatched designations—enhance not only functional clarity but also the visual rhythm of the scale.

In the lower portion of the dial appears the designation HOLOMETALLIC BAROMETER, accompanied by the word déposé, enclosed within an oval cartouche. The term holometallic is constructed from holo- (“entirely”) and metallic (“metal”), functioning as a marketing assertion of a “fully metallic” mechanism, implicitly contrasted with liquid (mercury) barometers. Notably, the term appears to combine two already established concepts: the holosteric barometer developed by PHBN (Naudet) and the metallic barometer of Eugène Bourdon.

The French word déposé is typically understood as meaning “registered” and indicates a registered trademark or design, a convention commonly employed by French manufacturers. When déposé is placed directly adjacent to a product name—as a distinct element, often within a cartouche or oval—it usually signals that the associated wordmark or graphic designation has been formally claimed as protected. In this context, the phrase Holometallic Barometer functioned as both a marketing and a legal identifier within the French instrument-making industry. However, it remains uncertain precisely when, and by whom, the designation Holometallic Barometer was first introduced.

The internal mechanism of the barometer features a characteristic “butterfly-shaped” construction: symmetrical brass plates with smooth, flowing curves form an elegant and airy architecture in which technical function is combined with a pronounced plasticity of form. One of the brass components bears the engraved marking Breveté S.G.D.G., indicating a French patent granted sans garantie du gouvernement—without government guarantee—a standard formula under nineteenth-century French patent law.

At the core of the construction lies an aneroid capsule measuring approximately 53 mm in diameter, made of copper or a copper-dominant alloy. Inside the capsule is a helical spring (positive magnetic test), designed to prevent the membranes from collapsing and to stabilise operation under varying atmospheric pressure. The capsule has a height of approximately 10 mm.

The movement of the capsule’s upper membrane, responding to changes in atmospheric pressure, is transmitted to the main lever with a substantial counterweight, into which a regulating screw is threaded, resting freely against the capsule membrane. From there, the impulse is conveyed to the main arbor and, via a small intermediate lever and a fusee chain, transmitted to the pointer arbor, ensuring a smooth and sensitive motion of the hand.

Particular attention is warranted by the construction of the main arbor. Rather than being rigidly fixed to the main plate, as is customary in traditional aneroid mechanisms, it is suspended on curved brass plates that form a distinctive supporting frame with integrated pivots and bearings for the rotating assembly. This frame incorporates a calibration screw, the head of which is accessible from the rear of the case. By turning this screw, the entire main arbor is raised or lowered, allowing precise adjustment of the instrument without direct intervention in the sensitive capsule assembly.

Overall, this Holometallic Barometer represents a striking example of the French aneroid tradition of the mid-nineteenth century—an instrument in which engineering ingenuity, patent culture, and visual restraint are united in a coherent and thoughtfully designed object, intended both for accurate observation of atmospheric pressure and for long-term everyday use.