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Object Overview
Before us is a Station barograph, manufactured approximately between 1960 and 1970 by the renowned German company R. Fuess, Berlin-Steglitz. According to the company’s catalogues, the instrument can be assigned by its construction to the basic model of the R. Fuess No. 78a Normal Barograph, although this particular example represents a more specialised version equipped with an oil damper, intended to suppress short-term mechanical and barometric disturbances. The maker’s plate on the case bears the name and the serial number .
B9110
brass, chrome, copper-beryllium, glass, paper, steel
The barograph is intended for the continuous recording of changes in atmospheric pressure over time. Unlike an ordinary indicating aneroid barometer, the position of the sensing element is continuously transmitted here to a recording mechanism, which traces a line on a chart mounted on a rotating clock drum. As a result, the instrument makes it possible not only to determine the current atmospheric pressure, but also to follow its behaviour over a given period of time, including the rate and character of its changes.
The construction of the instrument was designed primarily for stationary professional use. The base is cast from a light metal alloy, while the outer cover is made of steel. All principal external metal surfaces are finished in the characteristic grey hammered enamel widely used in the mid-20th century on laboratory, meteorological, and other precision technical instruments. This finish both protected the metal and effectively concealed minor signs of use.
A substantial rectangular chrome-plated carrying handle is mounted on top of the hinged cover.
Two windows are provided in the cover for observing the recording process. The main rectangular window is positioned on the front directly opposite the clock drum and allows the chart, the position of the pen, and the current pressure value to be seen. A second window is located in the end wall of the case and provides an additional side view of the drum. Both openings are glazed with flat mineral glass.
The base rests on four feet fitted with rubber shock absorbers. Each foot is mounted in a metal bracket provided with an additional fixing hole, allowing the barograph either to stand freely on a table or to be secured rigidly with screws to a work surface or bulkhead. The rubber elements also provide a degree of isolation from vibrations transmitted through the base.
On the left-hand side of the base is the recording drum with a brass outer shell. Inside it is an independent spring-driven clock mechanism that rotates the drum uniformly during the prescribed recording period. The mechanism is wound from above using a key fitted into the drum.
The clock-rate adjustment — advance and retard — is located beneath a small sliding dust cover in the base of the instrument.
A paper recording chart is wrapped around the cylindrical surface of the drum. Its edges are secured by a vertical spring retaining strip, which holds the paper closely against the drum surface.
The drum diameter is approximately 93.3 mm, while the usable recording height is 79 mm. The recording scale is approximately 0.75 mm per 1 hPa, and the stated accuracy is around ±0.3 hPa, consistent with the instrument’s role as a comparatively precise professional station recorder.
The chart is graduated both in time and atmospheric pressure. As the drum rotates, the recording pen moves vertically in response to changes in pressure, producing a continuous barogram.
To the right of the drum is the substantial sensing element: a vertical stack of nine aneroid capsules.
The capsules are made of beryllium bronze, a material particularly well suited to highly sensitive elastic diaphragms because of its combination of mechanical strength, stable elastic properties, and good fatigue resistance. Their external surfaces are coated with black protective lacquer.
Each aneroid capsule consists of a thin-walled, hermetically sealed metal chamber with corrugated walls from which the air has been evacuated. As atmospheric pressure changes, the capsules contract or expand slightly. Since the nine elements are connected in series as a single stack, the minute movement of each individual capsule is added together, producing a considerably greater longitudinal displacement of the complete sensing assembly.
This cumulative action provides the sensitivity required by the instrument without the need for excessively high mechanical amplification in the lever system.
Changes in the overall length of the aneroid stack are transmitted through a system of levers to the long recording arm.
A bimetallic strip is incorporated into the transmission system to provide temperature compensation. Its purpose is to counteract changes in the mechanical properties of the sensing element and transmission components caused by temperature variations, thereby maintaining accurate calibration of the barograph throughout its working range.
The long recording arm is made light yet sufficiently rigid to transmit the movement of the sensing element to the chart drum while imposing minimal load on the mechanism. Its suspension is of the so-called gate suspension type, a pivoted arrangement allowing exceptionally free movement of the arm with very little friction.
The pen is pressed against the chart primarily by the weight of the recording arm itself, without the need for a strong additional spring. This is especially important in a precision barograph, since excessive pen pressure against the paper would introduce additional resistance and could influence the position of the entire sensing system.
A correction screw and zero-tension spring are provided for adjusting the recording position so that the indication can be matched to a known atmospheric pressure value.
The instrument is also equipped with a separate pen-lifting device. This is actuated by a small lever on the base and allows the pen to be withdrawn from the chart, for example when changing the chart, removing the drum, or servicing the instrument.
An external button on the side wall of the case allows a time mark to be placed manually on the chart.
When the button is pressed briefly, the pen makes a small additional movement and draws a short vertical stroke on the barogram. Such a mark could be used by the observer to record the exact moment of a particular event, to check the time, to indicate a change of observer, or to correlate the barogram with other meteorological records.
Mechanically, the arrangement is simple and robust. When pressed by the finger, a steel bracket is forced against a rubber ring mounted directly on the shaft carrying the recording arm. The resulting small angular movement of the shaft is transmitted to the pen and produces the characteristic vertical mark on the chart.
The most interesting structural feature of this particular instrument is the presence of a separate oil damper, or dashpot, located immediately behind the stack of aneroid capsules.
Its purpose is to suppress short-lived movements of the sensing and transmission system that are not of interest as genuine meteorological changes in atmospheric pressure. Such disturbances may include mechanical vibration, shaking of the building, the slamming of doors, sudden air movements, and gusts of wind near the place where the instrument is installed.
Without damping, such disturbances could cause the sensitive capsule stack and the long recording arm to oscillate rapidly, producing unwanted spikes, thickened traces, or high-frequency deviations on the barogram.
The arrangement used in this Fuess instrument should be distinguished from the special damping systems employed in marine barographs, where the principal purpose was to suppress much larger accelerations and movements caused by the rolling and pitching of a vessel. Here the damper forms part of a stationary instrument and is intended primarily to smooth relatively small and short-lived disturbances.
The damper itself consists of a vertical metal cylindrical cup filled with a special damping fluid. The cup is closed at the top by a screw-on lid with a knurled outer rim. At the centre of the lid is a circular opening through which the movable piston rod passes.
At the lower end of the piston are three thin corrugated metal plates, or vanes, which are immersed in the fluid. When the piston moves rapidly, these plates force the surrounding liquid to move with them, creating hydrodynamic resistance. Slow changes in the position of the system, corresponding to natural variations in atmospheric pressure, are only minimally impeded, whereas rapid oscillations are effectively suppressed.
The damper therefore acts as a mechanical low-pass filter: it interferes very little with the slow meteorological signal while resisting rapid parasitic movements of the mechanism.
The piston rod is incorporated directly into the kinematic system of the barograph. It is pivotally connected to the shaft carrying the recording arm and is simultaneously linked, by means of a thin metal wire, to the shaft of the lever mechanism on the upper support. In this way, the resistance of the liquid acts specifically against relative movement within the transmission system without creating a permanent offset in the indication.
A knurled disc or nut is fitted to the upper end of the piston rod. Its function is connected, among other things, with servicing the damper: when the cup is being filled with fluid, the lid can be screwed onto the rod, facilitating correct assembly and manipulation of the mechanism.
The fluid used in such a damper must satisfy fairly strict requirements. It must retain a suitable degree of viscosity throughout the range of temperatures and humidity conditions to which it may be exposed, must not cause corrosion of the components, must remain chemically stable, and, most importantly, must not absorb water vapour from the surrounding air. A significant change in moisture content or viscosity over time would alter the damping characteristics and consequently the dynamic behaviour of the entire recorder.
This barograph clearly demonstrates the characteristic Fuess approach to professional meteorological instruments: the principal components are arranged as distinct functional units mounted on a substantial common base.
On the left is the clock drum, which determines the time coordinate of the recording. On the right is the stack of nine aneroid capsules, which converts changes in atmospheric pressure into mechanical displacement. Between them runs the long lever transmission, which amplifies this movement and conveys it to the pen. The bimetallic compensator corrects for temperature effects, while the oil damper suppresses rapid parasitic oscillations. The entire mechanism is enclosed within a rigid protective housing supported on shock-absorbing feet.
The result is not merely an ordinary domestic barograph, but an instrument designed for prolonged service in a professional meteorological station or other technical installation where stable, clear, and continuous pressure recording was required.
This R. Fuess station barograph is a characteristic example of the late period of classical mechanical meteorological recording, when traditional aneroid technology had already reached a very high level of technical refinement.
In its general architecture, the instrument corresponds to the basic Fuess No. 78a Normal Barograph, but the presence of a separate liquid damper makes this particular version considerably more interesting. The nine-element stack of beryllium-bronze aneroid capsules provides high sensitivity, the bimetallic system ensures temperature compensation, the carefully designed lever mechanism provides precise transmission of movement, and the hydraulic dashpot suppresses rapid parasitic oscillations that might otherwise impair the quality of the recording.
It is precisely this combination of robust industrial construction, the high sensitivity of the aneroid assembly, and an oil-damping system unusual for an ordinary station barograph that makes this example particularly representative of the technical evolution of R. Fuess instruments. It stands at the boundary between two eras: the fully mechanical meteorology of the 19th and first half of the 20th centuries, and the later period in which such highly developed mechanical recorders gradually began to give way to electrical and electronic recording systems.