Barometers Realm

Before us is a unique Miniature Goldschmid barometer, dating to approximately 1885, bearing serial number 1941, and manufactured by the Swiss maker Theophil Usteri-Reinacher (Zürich). The instrument is remarkable for its extremely small size — its dimensions scarcely exceed that of a €2 coin — making it one of the most compact high-precision barometric instruments of its time. Barometers of the Goldschmid system represent an improvement upon the aneroid design of the Vidie type: they dispense with conventional pointers and dials, and instead incorporate a micrometric screw, allowing for significantly higher precision in measurement.

The case is constructed as a compact cylindrical body in brass, likely finished with a protective lacquer, giving the surface its characteristic warm golden tone. The overall construction is notable for its dense and highly refined engineering layout.

At the top of the instrument is a rotating cap, controlling the position of the micrometric screw. Its surface carries a scale in silvered brass, graduated from 1 to 50. Each interval of ten is subdivided into 20 divisions, resulting in a total of 100 divisions across the full circumference, allowing precise registration of fractional turns of the micrometer. Integrated into this cap is a miniature arched mercury thermometer with a Celsius scale.

Mounted on the side of the case is an optical device — a small magnifier — intended for observing the primary measuring scale. This main scale is made of ivory, calibrated in millimetres of mercury, and resembles a register plate of a mercury barometer, albeit executed in an extremely reduced scale.

The instrument is fully mounted within an elegant case of Moroccan leather. The construction of the case includes hinged sections in brass, allowing the barometer to be used without removal, the instrument remaining in situ — a refined and practical solution characteristic of high-grade portable instruments.

At the heart of the instrument lies an evacuated aneroid capsule made from rolled, spring-tempered German silver, tensioned by a steel spring. The volumetric changes of the capsule, caused by variations in atmospheric pressure, are transmitted to a C-shaped spring with an extended platform, on which a brass plate is mounted by screws, with an agate bearing set at its centre.

Resting on this platform is the sharp, knife-like projection of a double lever, mounted on an axis and free to rotate about it. This lever consists of two parts connected near the pivot. The upper part forms an extremely thin steel spring with a flat polished surface, which, by its own elasticity, is pressed against the end of the micrometric screw. At the ends of this spring and of the lever itself are small flat pads, visible through a slot in the case, each bearing a finely engraved line at its centre.

Thus, both the lever and the spring carry a single horizontal index mark. By turning the micrometric screw, the mark on the spring is brought into exact alignment with the mark on the lever, using the magnifier mounted on the case. The pressure reading is then taken from the main barometric scale in millimetres of mercury, while fractional values are determined from the micrometer drum. The scale on the micrometric drum indicates the full turns of the screw.

Thus, this Goldschmid system barometer represents an outstanding example of late 19th-century precision instrument making and engineering miniaturisation, in which a complex measuring principle is realised in an exceptionally compact and elegant form. Such instruments occupy a special place in collections, reflecting the period’s pursuit of precision, portability, and mechanical refinement in scientific instruments.