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aneroid capsule tensioned on a C-spring
brass, glass, nickel silver, silvered brass, steel
Before us is a Watch-Pattern Pocket Aneroid dating to approximately 1920, retailed by the American scientific instrument company Keuffel & Esser Co. and most likely manufactured by the British firm J.H. Steward. The instrument represents a remarkable example of engineering functionality condensed into the compact pocket-sized form of a scientific instrument. In Keuffel & Esser catalogues, barometers of this type were marketed as instruments for surveying and mining applications, intended for determining atmospheric pressure and altitude under field conditions.
The form of the case deliberately recalls the familiar appearance of a pocket watch — an association characteristic of many portable scientific instruments of the late nineteenth and early twentieth centuries. Particularly expressive are the small suspension ring and the elegant knurled crown positioned at the top of the case, visually resembling the winding crown of a watch. Here, however, it performs an entirely different function, serving to operate the vernier mechanism and precisely adjust the altitude scale.
The case is manufactured from brass with a bronzed finish, now almost entirely worn away through time and repeated polishing, giving the surface a lighter tone of aged brass; traces of old oxidation remain preserved within the recessed areas. The construction is distinguished by pronounced simplicity and compactness: the flat rounded body fits comfortably in the hand or pocket while still retaining the substantial feel of a precision instrument.
At the front of the case is a rotating knurled bezel fitted with a flat mineral glass featuring a faceted edge. Inside the bezel is a movable index marker intended for recording pressure tendency, allowing the user to visually track changes in atmospheric conditions between observations, while also assisting in altitude measurements.
The dial is executed in silvered brass and displays an exceptionally restrained and functional composition. Its foundation is a concentric barometric scale calibrated in London inches of mercury over a range from 28 to 31 inches Hg, with each inch subdivided into hundredths, emphasizing the precision character of the instrument. The scale is supplemented by concise textual weather indications — “RAIN,” “CHANGE,” and “FAIR” — executed in thin capital lettering that scarcely distracts from the measuring portion of the dial. In the central zone appears the inscription Compensated, indicating temperature compensation of the mechanism, together with the retailer’s signature: “KEUFFEL & ESSER CO. NEW YORK.” At the lower portion is the marking “ENGLISH MAKE,” directly indicating the British origin of the movement itself.
The barometer is equipped with a vernier operating through a rack-and-pinion mechanism controlled by the crown positioned at the top of the instrument. Such a construction provides extremely precise adjustment and a high degree of measuring accuracy, enabling the user to register even the slightest atmospheric pressure variations under demanding conditions. The altitude scale of the vernier is calibrated in feet and extends to 5,000 feet.
The indicating hand is manufactured from blued steel and features a characteristic crescent counterweight, lending additional visual refinement to the dial composition.
The instrument operates through a temperature-compensated mechanism based on a nickel silver aneroid capsule tensioned on a C-shaped steel spring. Motion is transmitted to the hand arbor through a fusee chain system.
Overall, the instrument represents a characteristic example of a transitional period in which engineering instruments still retained the aesthetics of Victorian and Edwardian mechanics while already acquiring the compactness and practicality required for professional field use. The combination of British instrument-making and American engineering retail culture makes this aneroid not merely a functional scientific instrument, but also an expressive testament to the international culture of precision instrument manufacture in the early twentieth century.
