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brass, chrome, glass, ivory, leather, mercury, plastic, silvered brass, wood
This Fortin Barometer, dating from approximately 1955–1960 and manufactured by the British company F. Darton & Co. Ltd., is an exceptionally characteristic example of a post-war English scientific barometer, seemingly positioned precisely between two eras. Internally, it still remains a classical nineteenth-century Fortin barometer: featuring a traditional leather cistern, mineral glass, robust hand-crafted construction, and a working principle that had changed very little since the Napoleonic era. Externally, however, the instrument already fully belongs to the aesthetic of post-war scientific apparatus: industrial design, chromium-plated fittings, standardized instructions, an international dual-scale system, and the strict engineering visual language of the mid-twentieth century.
The name of Nicolas Fortin (1750–1831), the French mechanic and maker of scientific instruments, is inseparably associated with the development of high-precision mercury barometers. In 1809, Fortin introduced an extraordinarily successful design combining a glass cistern with a flexible leather base and an adjustable mercury level determined by means of an ivory pointer. This solution made it possible to establish the zero level precisely before every reading and dramatically increased the accuracy of scientific barometers. Instruments of this type became known as standard Fortin barometers and were used for more than two centuries by meteorological stations, observatories, physical laboratories, universities, and schools throughout the world.
The barometer is mounted on a substantial hardwood mounting board, most likely African mahogany (Khaya or a related species), finished with industrial lacquer. The wood displays a characteristic long-fiber grain with a warm reddish honey-colored tone. At the upper part of the board is a hook from which the barometer is suspended by a chromium-plated hanging ring and additionally secured with a screw. At the lower part is a supporting ring into which the cistern reservoir is inserted and likewise fixed with three screws.
Particularly interesting are the two white plastic reflector inserts recessed into the thickness of the wooden board. The material appears to be an early engineering plastic, most probably rigid white PVC, widely used in British laboratory equipment during the post-war period. The upper insert is positioned behind the barometric scale and serves to facilitate precise reading of the mercury level. Opposite this insert, the cylindrical body of the barometer is cut with two narrow vertical apertures allowing light to pass through the glass cylinder and reflect from the white surface, thereby creating a contrasting background for observing the mercury meniscus. The lower insert is positioned behind the glass cistern and is used for visually controlling the mercury level during zero adjustment.
The long tubular brass body of the barometer, measuring only approximately 25 mm in diameter and enclosing the barometric tube, is finished in black and fitted with chromium-plated hardware and screws. At the upper section, this cylindrical tube carries a silvered surface upon which the barometric scale is engraved. Here are located the previously mentioned twin vertical observation apertures, positioned opposite one another like the eye of a needle, allowing the mercury meniscus to be observed. For precise readings, a vernier scale is installed between these two apertures and operated by a large knurled chromium-plated knob positioned slightly lower on the корпус. The vernier permits readings to an accuracy of 0.002 inches or 0.05 mm.
An interesting feature of the instrument is the presence of two parallel barometric scales. To the left of the tube aperture is a metric scale in millimeters of mercury ranging from 670 to 820 mm, while to the right is an English scale in London inches of mercury ranging from 27 to 32 inHg.
At the upper section of the scale is engraved the well-known Darton logo in the form of a dart, beneath which appears the number L1186. Judging by its position and manner of execution, this number is most likely not a serial number, but rather an internal model designation, drawing reference, or catalogue type number used by F. Darton & Co. Ltd. to identify this particular Fortin barometer design.
The entire upper scale section is enclosed within a long cylinder of mineral glass, providing excellent transparency while protecting the scale and barometric tube from dust and mechanical damage.
In the central part of the body is a mercury thermometer mounted upon a silvered brass plate. Interestingly, the thermometer scale is not engraved on the metal plate but instead applied directly to the glass body of the thermometer itself. The scale is calibrated in degrees Celsius over a range from –10 to +50°C. The lower portion of the thermometer, containing the mercury reservoir, is slightly curved inward and extends deeper into the body toward the barometric tube.
The barometric tube itself measures approximately 86 cm in height and about 10 mm in diameter. It contains a substantial volume of mercury — approximately 40 ml — while the total mercury content of the instrument approaches one kilogram in weight (70 ml). The narrowed lower end of the tube is secured into a boxwood cistern cap.
The visible portion of the cistern consists of a thick polished cylinder of mineral glass, allowing the mercury level to be clearly observed. Attached to the inner side of the cap is a downward-pointing ivory cone. This point serves as the zero reference level. Before taking a reading, the mercury level in the cistern is raised or lowered by means of the adjustment screw until the mercury surface just touches the tip of the ivory pointer. This system, introduced by Nicolas Fortin in the early nineteenth century, made extremely precise measurements possible and continues to be employed with only minimal modifications to the present day.
The complete construction of the cistern is particularly interesting. It consists of a cylindrical glass lantern covered by a thin boxwood cap into which the barometric tube is inserted. Below this is a cylindrical boxwood body connected to a chamois leather mercury reservoir. The entire assembly is enclosed within a protective brass cylinder painted black. The adjustment mechanism consists of a long chromium-plated screw operated by a knurled chromium-plated control knob located at the lower end of the cistern. Rotation of this screw drives an internal boxwood pressure piece positioned above the leather reservoir. As pressure is applied, the leather mercury bag is compressed, thereby raising or lowering the mercury level within the cistern. All these components are firmly compressed between two brass body plates and secured by three chromium-plated screws with spherical heads.
Upon the protective cistern cylinder appears the inscription: “Standard Conditions: g = 980.665 cm/s²; Temp = 0°C”, indicating the standard conditions to which the barometer scale has been calibrated — namely standard gravitational acceleration and the reference mercury temperature of 0°C. Such marking emphasizes the scientific and metrological nature of the instrument, designed for precise atmospheric pressure measurements with temperature corrections and standardized physical conditions taken into account.
This Fortin Barometer by F. Darton & Co. Ltd. represents a remarkable example of the late evolution of the classical mercury barometer — an instrument in which engineering solutions developed at the beginning of the nineteenth century continued to exist within the post-war scientific aesthetic of the mid-twentieth century. It simultaneously preserves the archaic physical beauty of the traditional mercury barometer while demonstrating the strict functionalism of British laboratory apparatus from the era following the Second World War.
