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self-elastic stacked capsule movement
aluminium, beryllium, brass, cast iron, copper bronze, glass, nickel-plated brass, steel
This WWII Precision Aneroid Barometer, dating to circa 1938 and manufactured by the renowned German firm R. Fuess, represents an exemplary specimen of the German precision instrument-making school of the wartime period: austere, functional, devoid of decorative compromise, and focused exclusively on accuracy and reliability.
The instrument is housed in a strictly cylindrical case made of nickel-plated brass, giving it a distinctive cold metallic sheen while simultaneously providing resistance to corrosion and mechanical stress. At the top, the case is fitted with a suspension ring, intended for stationary mounting in laboratory, headquarters, or field conditions. It is likely that the barometer was originally supplied with a protective carrying case, which has not survived.
The front of the case is closed by a thin bezel made of the same nickel-plated metal. The bezel retains a flat mineral glass and is rigidly secured to the case by three evenly spaced screws around the circumference. This construction eliminates play and ensures stable positioning of the glass under vibration and temperature fluctuations—an essential requirement for precision measuring instruments.
The dial is made of aluminium and features a matte, light-coloured surface designed to minimise glare. It carries a concentric barometric scale calibrated in millibars (mb) over a range of 920–1080 mb, corresponding to professional meteorological standards and allowing operation across both deep low-pressure systems and high-pressure regions. The scale is entirely free of decorative elements and intended solely for analytical reading.
On the left side of the dial is an embossed Reichsadler emblem—an eagle holding a wreath enclosing a swastika. During the period in question, this symbol was used as a marker of property belonging to state institutions of the Third Reich. Its presence on the dial allows a well-founded assumption that this barometer was intended for use within governmental or military organisations. The most probable context of operation is the military weather services (Wetterdienst) serving the army, Luftwaffe, or naval forces, where high-precision barometers were essential for meteorological forecasting, flight operations, artillery calculations, and naval missions.
In the lower third of the dial appears the abbreviation D.R.P., standing for Deutsches Reichspatent (“Patent of the German Reich”). This marking indicates that the design of the instrument—or specific components thereof—was protected by a state patent, a characteristic feature of R. Fuess products, reflecting the company’s strong engineering culture and involvement in the development of reference-grade measuring instruments.
Notably, the dial is completely devoid of any textual weather indications such as “Stormy” or “Fair.” This is a defining feature of precision barometers: such inscriptions are empirical and simplified in nature and do not reflect actual meteorological conditions. In professional practice, they are considered superfluous and potentially misleading.
Between the glass and the dial is installed a corrugated metal ring serving two functions simultaneously. First, it acts as a reflective ring, improving the legibility of the scale under oblique lighting. Second, owing to its spring-like properties, it functions as a dial retainer, securely fixing the dial within the case without the need for additional fasteners.
The pointer exhibits a distinctive engineering form: a slender body combined with a pronounced bend and a thickened hub, reducing inertia and improving the responsiveness of the mechanism to pressure changes. This geometry is typical of instruments designed to register rapid and minute fluctuations.
The barometer mechanism itself is a high-sensitivity aneroid assembly incorporating a stack of six self-elastic capsules, a rack-and-pinion transmission to the pointer shaft, and a system of levers amplifying the motion of the capsule membranes. The aneroid capsules are manufactured from beryllium bronze (Cu–Be)—a copper alloy containing approximately 1.5–2 % beryllium, sometimes with small additions of nickel or cobalt. Their dark, nearly black appearance is the result of both manufacturing processes and age:
The choice of beryllium bronze was dictated by its exceptional properties: high elasticity without creep, minimal hysteresis, dimensional stability under cyclic loading, high fatigue strength, and excellent thermal stability—critical attributes for aviation and artillery applications.
Increasing the number of capsules to six reduces the specific load on each membrane while simultaneously increasing the total displacement of the stack in response to changes in atmospheric pressure. This solution is characteristic of instruments intended either for enhanced accuracy or for stable long-term operation under demanding conditions.
Atmospheric pressure acts upon the entire capsule stack, causing axial compression as pressure rises and expansion as it falls. The movement of the stack is transmitted via a central stem to a system of levers and an intermediate shaft. Unlike fusee-and-chain mechanisms, this design employs a toothed rack engaging a pinion rigidly mounted on the pointer shaft.
This arrangement provides a more direct and compact transmission of motion, reduces the number of elastic elements in the kinematic chain, and eliminates typical issues associated with chain drives, such as wear and uneven tension. At the same time, transmission accuracy is preserved through carefully chosen lever ratios and minimal clearances in moving joints.
The lower end of the aneroid capsule stack is rigidly fixed in the base of the mechanism. By means of an adjustment screw, the effective lever arm of the brass plate positioned above can be altered, thereby increasing or decreasing the overall sensitivity of the mechanism.
When atmospheric pressure increases, the capsule stack compresses and, through the lever system, displaces the rack, rotating the pointer shaft toward higher readings. When pressure decreases, the capsules expand, the rack moves in the opposite direction, and a spiral spring maintains constant tooth engagement, preventing backlash and dead play.
The entire mechanism is mounted between two massive steel side plates, connected by brass spacer tubes. This rigid frame construction ensures precise axial alignment, high structural stiffness, and resistance to deformation—qualities especially important for instruments intended for official or institutional use.
This R. Fuess barometer constitutes a genuine document of its era, in which engineering ingenuity directly served state and military objectives. The presence of patent protection, a standardised professional scale, and a state emblem attests to the instrument’s integration into the centralised systems of supply and operation characteristic of the military meteorology of the Third Reich.
Such barometers were never intended for private interiors or decorative purposes; their role was to provide accurate and reproducible measurements in the service of aviation, naval operations, and ground forces. In this sense, the present example should be regarded not merely as a specimen of high-class instrument making, but as a rare historical artefact directly connected to the functioning of one of the key infrastructures of a wartime state—the system of meteorological observation and forecasting.
