Barometers Realm

This laboratory wall-mounted Gay-Lussac siphon barometer, produced by Analis in the mid-20th century, was used in universities and meteorological stations. The barometer’s base, in a warm light-brown tone with a subtle yellowish hue, shows the fine, close-grained texture typical of beech wood (Fagus sylvatica). Beech was traditionally chosen for laboratory barometer and manometer panels due to its high dimensional stability under varying humidity and its ease of finishing. The mercury-filled barometric tube is mounted on the wooden board within a supporting metal frame.

This type of siphon barometer was invented in 1816 by the French chemist Joseph-Louis Gay-Lussac. Its distinctive feature is the unusual zigzag-shaped glass tube. The upper and lower limbs of the siphon, each 11 mm in diameter, are almost coaxial and connected by a narrower tube (8 mm in diameter). Near the lower bend, a strong capillary constriction is formed to reduce oscillations of the mercury level and thus damp its inertial movement. The connecting tube between the two limbs contains two Bunten traps designed to capture any air bubbles that may accidentally enter the mercury column. The lower limb, open to the atmosphere, is fitted with a threaded metal socket that allows the attachment of a removable plug, an adapter, or a filtering washer, as well as the option to connect a manometric adapter.

A long chrome-plated scale, running almost the entire length of the barometric tube, is graduated in centimeters of mercury from 0 to 80. Two verniers mounted on a rack-and-pinion mechanism with knurled adjustment knobs allow fine readings. One vernier corresponds to the upper limb of the siphon, the other to the lower. The atmospheric pressure is obtained by subtracting the lower reading from the upper. The mercury level in the lower limb represents the zero point of the scale, from which the height of the mercury column is measured. Each vernier features a small “sight frame” for precise alignment with the mercury meniscus. The viewing slit contains a fine horizontal wire in its center; this optical alignment type of vernier ensures accurate readings without parallax error, which occurs when viewing at an angle.

The barometer is also equipped with a mercury thermometer on a white plastic base, graduated in degrees Celsius. The frame includes four mounting holes—two at the top and two at the bottom—for secure wall installation.

This well-crafted scientific instrument exemplifies the precision and aesthetic simplicity of mid-century European laboratory design, uniting functionality, accuracy, and enduring craftsmanship.