Barometers Realm

The interior is arranged as a so-called “weather cabinet.” The principal visual field is occupied by a paper register plate. Running centrally through the cabinet is the mercury barometer tube, secured by four gilded brass mounts that hold it neatly against the printed scale. In the lower section, two additional instruments complement the system: to the left, a storm glass accompanied by an explanatory instruction plate, and to the right, a mercury thermometer.

The barometric scale occupies the upper portion of the register plate and is calibrated in London inches of mercury over a range from 27 to 31 inches. On either side of the scale appear the characteristic FitzRoy indications linking pressure to wind direction and weather conditions, along with labels for setting the “yesterday” and “today” indicators. This reflects the typical FitzRoy approach, in which absolute pressure values are of secondary importance: the user records the current level and observes its change over time. It is precisely this dynamic—rising or falling—that forms the basis of the forecast.

To facilitate this comparative reading, the instrument is equipped with two index pointers corresponding to “set yesterday” and “set today.” These are controlled via a rack-and-pinion mechanism operated by two brass knobs positioned on the front of the case. This arrangement allows for easy adjustment and comparison, turning the act of observation into a clear and almost mechanically structured process.

Below the main scale are two elongated panels titled “Admiral FitzRoy’s Special Remarks”. These texts constitute a condensed system of practical interpretative rules derived from FitzRoy’s own work. At this point, the instrument transcends its purely measuring function and becomes a kind of wall-mounted “weather manual,” offering the user a ready-made interpretative framework.

The register plate itself, made of paper and protected by a varnish layer, was produced by lithographic printing by Maclure, Macdonald & Macgregor, Lith., one of the largest and most technologically advanced lithographic firms in nineteenth-century Britain. Founded in Glasgow in 1835, the company rapidly expanded beyond its regional origins into a large-scale industrial enterprise with branches in London, Liverpool, and Manchester, serving a national market. By the mid-century it had become a major force in the production of visual material for science, commerce, and government, its status confirmed by the official title “Lithographers to the Queen,” attesting to its high level of quality and trust.

In the context of Victorian instrument-making, such firms played a crucial role in shaping the visual language of scientific devices, including scales, instructions, explanatory texts, and decorative elements. In FitzRoy barometers this role is particularly significant, as much of the instrument’s function lies not only in measurement but in the interpretation of readings through printed guidance. The lithographed plate thus functions not as a secondary component but as a true “interface” of the instrument.

Technically, the plate was produced using industrial lithography, a planographic printing process based on the chemical contrast between hydrophilic and grease-receptive areas of the printing surface. Of particular importance is the fact that Maclure, Macdonald & Macgregor were among the first British firms to introduce steam-powered lithographic printing. Unlike earlier hand-operated lithography, where each impression required considerable manual effort, steam power mechanised both pressure and paper handling. This greatly increased production capacity, reduced cost, and ensured a high degree of consistency—an essential condition for the serial manufacture of scientific instruments.

The storm glass, located in the lower section of the cabinet, is a separate sealed chemical indicator. The instruction plate beneath it explains its interpretation: a calm, low deposit indicates fine weather; feather-like crystallisation suggests rain; a higher rise with moving white particles indicates strong wind or storm. Although such devices predate FitzRoy, it was he who systematised and popularised their use. At the same time, his 1859 guide already noted that storm glasses are influenced by factors beyond pressure and temperature. In this instrument, therefore, the storm glass should be understood as a visually engaging auxiliary device, while the primary measuring function remains with the mercury barometer tube.

The barometric tube itself is of the bulb cistern type. The mercury reservoir, situated on the lower bend of the siphon tube, is formed as a small glass bottle fitted with a stopper into which a steel pin is inserted, allowing the bore to be closed during transport. The tube has a substantial external diameter of approximately 14 mm and an internal bore of about 4 mm, ensuring clear readability and stable performance.

In the lower right section is a mercury thermometer with a teardrop-shaped reservoir. Its scale is calibrated in degrees Fahrenheit and engraved on a plate of horn or ivory mounted onto a wooden backing, providing both contrast and durability.

Taken as a whole, this barometer is significant not only as a finely crafted decorative object but also as a historical document. It represents a brief yet crucial phase in the commercialisation of FitzRoy’s ideas in London: the transition from an almost “official” language of weather forecasting to a marketable interior object designed for private use. In this instrument, measurement, instruction, visual culture, and industrial production are brought together into a single system, making it not merely a device, but a tangible expression of how nineteenth-century science entered everyday life.