Very scarce 8” open dial twin thermometer aneroid or holosteric barometer by Naudet et Cie, France c1900

Holosteric barometer having 7¾” silvered die struck open dial, the upper part annotated with standard meteorological terms, semicircular barometric scale calibrated in inches of mercury with a range from 28” – 31” and divided to 1/50th” with stations on the inch, further marked “Holosteric Barometer” with “PHBN” logogram at centre, and “Made in France.”

The lower part with twin thermometers: the left hand, curved red alcohol thermometer with register above marked “Centigrade Thermometer” and calibrated in Centigrade with a range from -10 to 50, register below marked “Reaumur” with a range -10 to 40; the right hand curved mercurial thermometer set on a Fahrenheit scaled register marked “Fahrenheit Thermometer” above and “Fahrenheit” below, with a range from 20 to 120, the scale split both sides. The inner dial with brass trim ring finisher.

Substantial 1st quality display movement driven from a 2.8” single nickel alloy capsule and tensioned on a plated and polished C spring, milled upper surface to bridge, blued screws. Blued steel pointer, gilt index, silvered reflector ring, bevelled glass.

All contained within a classical Naudet pattern scalloped case, extension post and suspension ring. The verso with “PHBN” logogram to centre. Calibration port.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions. The movement working well showing a maximum error across the scale of less than 0.03”, highly sensitive with good progression.

Generally very crisp, the dial with very minor ageing. Both thermometers intact and working precisely – of particular interest is the alcohol thermometer which retains very good density to its red pigment, very often these are bleached and almost transparent. The original glass clean and damage free as inspected by the naked eye. The case clean and essentially damage free with good colour.

Comments: These Naudet holosteric barometers were unequivocally the best in their class for this time. It is testament to the skill in manufacture and design that it is still able to maintain such a comparatively high performance specification.

Very infrequently seen with the twin thermometers and in this size, and generally when they do occur, sadly have been neglected and abused. This example is unquestionably the one of the finest we have worked on.

High aesthetic value with practical function and a fine commentary on the best in barometer making. Very much a collector’s piece.