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Object Overview
This unique Goldschmid’s Precision Leveling Barometer, serial number 4251, dating to around 1900, was manufactured by Theophil Usteri-Reinacher (successor to Hottinger & Cie, which in turn had succeeded Jakob Goldschmid). It represents an advanced refinement of the aneroid barometers originally invented by Lucien Vidie. Goldschmid’s barometers were renowned for their extraordinary precision, comparable to mercury barometers, and were primarily used for measuring barometric altitude by mountaineers, explorers, and engineers in railway and road construction.
The barometer consists of a brass drum with a rotating lid at the top. Engraved on the lower edge of this lid is an auxiliary scale divided into 100 increments. At the center of the lid is mounted a micrometer screw, which acts on two levers below; the ends of these levers are visible externally through a longitudinal slot in the instrument’s casing. Each lever carries a fine horizontal line, serving as index marks for the barometric scale, which is calibrated in millimeters of mercury (within a range of 600–850) on an ivory plate located to the right of the slot.
4251
micrometric
brass, glass, ivory, jewels, leather, nickel silver, paper, steel
For precise adjustment, a magnifying lens is employed, set at an angle to the graduated scale so that the index lines and scale divisions can be brought into exact alignment. The lens is mounted in a nickel-plated brass holder, which can be screwed in or out to adjust the focus to the observer’s eye, and which also rotates around its axis, allowing the magnifier to follow the markings along the length of the slot.
To take a reading, the drum lid with its auxiliary scale is rotated clockwise. In doing so, one of the elastic indicator rods is gradually lowered until it aligns with the other rod. The atmospheric pressure value in millimeters of mercury is first read from the ivory scale; then, for greater precision, the auxiliary scale on the drum lid, divided into 100 parts, is used. Each interval corresponds to 1/100 mm of mercury, thereby providing additional decimal places for the reading.
At the heart of the barometer lies a sensitive aneroid capsule made of nickel silver, tensioned by a steel C-spring, which transmits its motion to a pivoting lever. Attached to this lever is a delicate contact arm that engages with the micrometer screw. These are the very tips of the lever and arm visible in the casing slot, whose end surfaces must be brought into coincidence in order to take a measurement.
As a hard and wear-resistant bearing surface for the lever and arm with their indicator rods, a ruby (corundum) stone is used. Thanks to the exceptional hardness of corundum, friction is minimized and long-term durability of the instrument is ensured.
The barometer is also equipped with a small mercury thermometer, built into the instrument’s casing and graduated in degrees Celsius. In addition, inside the barometer’s lid, beneath thick faceted mineral glass, is a printed correction table. More detailed correction tables are provided in a small booklet supplied with the instrument.
The barometer is housed in a protective case covered with leather and lined inside with violet velvet. The uniqueness of the case lies in its three-part construction: it opens on hinges so that the barometer can be freely used without removing it from its housing. In fact, the instrument was not intended to be used outside its case, since it is secured to the case with two screws.