A rare four glass mahogany cased micro-barograph by Negretti & Zambra No 2049 retailed by Turnbull & Co, Edinburgh c1910

Micro-barograph constructed principally in lacquered brass at large scale, the movement comprising nine-capsule pressure sensing unit mounted to a sub chassis brass spring plate, bi-metallic temperature compensated primary lever, polished steel spindles and drop link, grained and lacquered steel cross beams, polished aluminium recording arm, all raised on four substantial pillars over a full length chassis stamped with serial no. “2049.”

Mercurial thermometer set on a grained and silvered register calibrated in degrees Fahrenheit and Celsius with corresponding ranges of 20° to 120° and -10° to 50°. Calibration spindle, ink station with bottle and dipper. Arrestor bar. Substantial 7″ x 5″ recording drum, captive key, paper spring clip, the base stamped with instrument serial no. “2049.”

All maintained within a good quality mahogany four glass case with mirrored back, hinged cover and frieze drawer. Plate with retailer’s details “Turnbull & Co, 60 Princes St, Edinburgh.”

Condition: The subject of a full service, conservation, and calibration under laboratory conditions. The movement working very well across the standard range, but low at the extremes, normal for instruments of this period.

The movement survives in exceptional condition, retaining most of its original finish with deep colour and vibrancy, some patches of oxidation to drum cover, minor ink staining to chassis below arm, the ink station re-lacquered, the recording arm a bespoke in-house replacement to the exact original pattern, the nib replaced.

The timber case generally cleaned, the base back with some restoration otherwise retaining most original lacquer. The original mirror with obvious deterioration to silvering – this has been left as is in the interests of originality, but would be easy to replace with mirrored or clear glass.

Comments: The micro-barograph is little known and far less understood – put simply, this instrument is just spectacular both in scale and in terms of resolution, the detail in the trace on a standard barograph magnified by a factor of two! This often means that where no perceptible pressure change is evident on a regular instrument it is clearly shown on a micro-barograph and because of this, these larger barographs were often used in meteorological environments where very fine accuracy was desired, or in locations such as the Tropics where pressure fluctuations are generally slight.

This instrument is one of a series of the first in-house barographs made by Negretti & Zambra, taking many of the design cues from Richard Frères and clearly making a real effort to match the very high standard of engineering found in the French-made instruments. More details of this discussion can be found here.

Listed in Negretti & Zambra’s catalogue of 1910 as item “82,” this is simply described as a larger Self-Recording Aneroid Barometer – the term “micro-barograph” seems to have been coined around 1920, possibly by Short & Mason.

This antique micro-barograph is an instrument for the serious collector, one without which no collection could be said to be complete.