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A328-26 · Aneroid
c.1880
Object Overview
This is the Carved Foliage Aneroid Barometer, a magnificent wall-mounted aneroid barometer with thermometer, made around 1880 and housed in a richly decorated wooden case with expressive naturalistic carving. The dial is signed by A. Krüss, Hamburg, a well-known Hamburg firm that made and sold optical, physical and scientific measuring instruments. Krüss is not the maker of this barometer. The firm may have carried out the final assembly using some of its own components together with parts from specialist makers, and it acted as the retailer. Of particular interest is the aneroid movement inside, whose design corresponds to a rare type associated with the Hamburg optician D. Brauckmann. This exceptionally attractive and carefully made movement has historical and technical value in its own right and is the true heart of the instrument.
Lessing-Brauckmann
brass, cardboard, carved wood, cast iron, glass, opal glass, steel
The exterior of the barometer is no less remarkable. Its large, vertically elongated case is a complex sculptural composition made up almost entirely of plant motifs. In its execution it belongs to the tradition of German decorative carving of the second half of the 19th century, close to the so-called Black Forest style. This tradition is characterised by naturalistic depictions of leaves, branches, flowers and woodland animals, by intricate openwork compositions, and by the aim of turning an ordinary household object into a work of decorative art in its own right.
The case is most likely carved from solid walnut, a common material for fine sculptural carving. The composition is executed mainly in hand-cut relief and pierced carving, with deeply cut-back grounds and careful working of individual details. The surface is a rich dark brown with warm reddish tones and the soft sheen of a polished finish. A darker patina remains in the recesses, further emphasising the depth and intricacy of the carved ornament.
The composition is crowned by a huge fan-shaped leaf spread wide above the centre of the case. Its form recalls a stylised acanthus leaf, one of the most widespread plant motifs in European decorative art. The broad blade is divided into several rounded lobes, each decorated with fine, deeply cut veins radiating from the central base. Thanks to the high relief and varying depth of carving, the leaf looks three-dimensional, as if slightly curved and unfolding towards the viewer. Directly beneath it are symmetrical scrolls that turn into elongated lateral plant elements.
The upper part of the case gradually narrows towards the central thermometer section. This section is framed by curved elements resembling tree branches or young shoots with curled tips, which rise on either side of the thermometer to form a kind of natural frame. The surface of the branches is covered with longitudinal grooves imitating wood grain, and their upper ends finish in expressive spiral scrolls. Between them lies a narrow vertical recess holding the thermometer, whose pale scale stands out clearly against the dark wood.
Below the thermometer begins the densest part of the carved composition, surrounding the round barometer case. Here are four large carved leaves, noticeably different from the broad fan-shaped crest. They are elongated and pointed, with a pronounced central vein and numerous lateral veins. Their silhouettes resemble long leaves with wavy, in places curled, edges, rendered with great naturalistic conviction.
At the very bottom, diagonal branches cross and end in a small, expressive knot of intertwined shoots. This detail resembles a tied knot or a tightly rolled twig and serves as the decorative conclusion of the whole composition.
The round aneroid barometer is set in a projecting metal mount in the lower part of the wooden case. Its smooth brass bezel, with a warm golden tone, contrasts strikingly with the dark carved wood. Unlike ordinary barometers, whose solid dial hides the movement, this one has an open dial through which much of the internal mechanism can be seen directly. This gives the instrument a particularly attractive technical appearance: the many brass parts, the steel arbors and the large corrugated aneroid capsule all become part of its decoration.
The dial itself is made of card: a white ring mounted on a thin zinc plate. It is printed with two parallel concentric barometric scales in different units of atmospheric pressure.
The outer scale is graduated in Paris inches of mercury (Pariser Zoll), a historical unit widely used in continental Europe before the metric system was finally adopted. It covers the range from 26 to 30 Paris inches, with each inch divided into 24 equal parts. The smallest division is therefore 1/24 of a Paris inch, approximately 1.128 mm of mercury.
The inner scale is metric, divided in centimetres of mercury and covering the range from 71 to 81 cm. With two parallel scales, atmospheric pressure can be read in both traditional Paris inches and metric units. This combination is characteristic of the transitional period, when the metric system was already widely used in science but the older units were still current in everyday life and in many technical publications.
The dial also carries traditional weather indications in German. The words Stürmisch (stormy), Wind und Regen (wind and rain), Veränderlich (changeable), Schön Wetter (fine weather) and S. Trocken (very dry) are placed along the corresponding sections of the barometric scale. They reflect the widespread 19th-century tradition of marking weather conditions directly on the dials of domestic barometers.
The indicating hand is made of thin blued steel. Its long, extremely narrow tip allows precise reading against the fine divisions of the scale without obscuring them. The opposite end of the hand is decorated with an elegant crescent.
The dial and open movement are protected by a thick flat mineral glass set in a round brass bezel. Mounted at the centre of the glass is a separate brass set hand that indicates the pressure tendency. It is not connected to the aneroid movement and is moved by hand, serving to compare the current reading visually with the previous one. Its tip repeats the outline of the main steel hand, which is relatively rare, so the two hands form a stylistically matched pair despite their different materials and colours. The set hand is turned by a knurled brass knob.
Directly above the barometer, in the narrow central part of the carved case, is a mercury thermometer for measuring the ambient air temperature. It consists of a fine glass capillary with a mercury bulb at the bottom, mounted on an elongated plate of white opal glass. The milk-white opal backing keeps the fine divisions and black numerals easy to read even in fairly dim light, while creating an elegant contrast with the surrounding dark wood. The thermometer has two parallel temperature scales: Fahrenheit (°F) on the left and Centigrade on the right.
The movement is built on a massive cast-iron frame, cast as a ring with three spokes converging on a central hub. Three forked, slotted lugs serve to mount the movement. Cast pillars carry a brass annular plate, screwed to them with steel screws. The heavy, rigid frame closes the load path between the capsule support and the lever bearings, since any flexing of it would affect the readings.
The movement is designed to be seen. The plate, bridges and bearing pillars are brass, the bridge screws and the main lever arbor are blued steel, and the bearing pillars are topped with pointed finials.
The sensing element is a single large corrugated aneroid capsule of a yellow copper alloy, probably brass. The upper diaphragm and the rim are silvery white, most likely a nickel- or silver-plated finish on the visible side of the capsule. A notable feature is the way the two diaphragms are joined into a single capsule: the upper wall overlaps the lower one and embraces it with its flange. The solder was drawn into the gap by capillary action as a thin film, which is why it cannot be seen.
The capsule has no internal spring to keep its walls from collapsing, and since no massive external springs are visible either, it is tempting to call it self-springing. However, there is in fact a spring here, and it performs an extremely important function, discussed below. The capsule certainly has some self-springing properties, but these come mainly not from the type of material but from the combination of work-hardened sheet, thick walls and deep corrugation.
A slotted post is fixed at the centre of the upper diaphragm, and a link made of blued steel strip is fitted into the slot. The other end of the link is pivoted to the main lever close to its arbor. The pivoted link transmits the movement of the diaphragm in both directions. This connection allows the lever the angular movement it needs without creating significant bending force where the link is attached to the diaphragm.
The main lever is a separate moving part mounted on its own transverse, spindle-shaped arbor of blued steel. The pointed ends of the arbor turn in centre bearings with adjustable screw centres, which are screwed into shaped pillars on the radial bridges of the plate. The lever has two arms. The long arm is 2.5–3 times the length of the short one; it is S-shaped, reaches past the arbor of the bell-crank lever and is connected to it at its end by a pivoted link. The ratio between the length of the main lever and the small radius at which the capsule link is attached forms the first stage of multiplication.
A small, curved, two-armed leaf spring working in bending passes through the central area of the short arm of the main lever, and its free ends bear against a fixed shaped brass plate. There is thus an elastic connection between the moving lever and the fixed support. When the capsule contracts and turns the main lever, the central part of the spring moves relative to its supporting ends. The curvature of the spring changes, creating additional elastic tension, and the resulting force tends to return the lever to its original position.
In this case the spring takes a direct part in establishing the mechanical equilibrium of the sensing system. This is what suggests that it is the main counteracting spring of the aneroid. In other words, it performs the function of the aneroid's main force spring, replacing the traditional massive C-spring or an external coil spring.
The capsule is subjected to a considerable force from atmospheric pressure. This force is transmitted to the main lever at the point where the lever is connected to the upper diaphragm. At some distance from this point lies the lever's axis of rotation, and on the opposite side is its short arm with the leaf spring. Since the two forces act at different distances from the axis, equilibrium requires only that the moments they create be equal.
Brauckmann thus separated two functions:
In this arrangement the main lever is no longer merely a transmission link. It becomes part of the system that mechanically balances atmospheric pressure.
The rest of the transmission differs little from the traditional arrangement. The bell-crank lever turns on its own arbor in the same pointed pivot screws, and, as already mentioned, the link from the main lever is pivoted to it. From the vertical output arm of the bell crank, an ordinary thread runs to the pointer arbor, turning the arbor and with it the indicating hand. A flat spiral hairspring of blued steel, fixed by its inner end to the arbor, keeps the thread under constant tension.
A special feature is the third arm of the bell crank, which points inwards and carries a counterweight of unusual form: a tightly wound coil on a threaded rod, held by a knurled nut. This appears to be an adjustable, self-locking weight: the coil provides the mass and at the same time locks the nut, while moving the nut finely alters the static moment of the lever.
The movement has an interesting calibration system. An adjusting screw is screwed into the hub of the cast-iron frame at the back, accessible through a hole in the rear protective panel. It acts on the rigid centre of the capsule's lower diaphragm through an intermediate part, apparently an elastic element that takes up play in the thread. Turning the screw shifts the whole capsule along its axis, and with it, through the transmission, the hand.
To sum up, Brauckmann replaced the traditional massive C-spring with a small two-armed leaf spring placed on the short arm of a main lever mounted on its own arbor, and used the mechanical advantage of the lever to reduce the force required of this spring. This freed the space above the capsule and resulted in a very compact design that is at once elegant and functional.
This barometer is not merely a decorative wall instrument but a rare and expressive example of late 19th-century European scientific and technical craftsmanship, in which artistic carving, precision mechanics and traditional meteorological practice come together in a single harmonious composition. Its historical value is enhanced by the combination of the signature of the well-known Hamburg firm A. Krüss with the unusual movement design associated with D. Brauckmann. This makes the instrument an interesting record of the cooperation between specialist instrument workshops and the retail firms of its time.