Atmos Barometer of grained and lacquered brass construction with silvered and engraved brass twin dial/registration plates of rectangular form: the outer having calibrations from 28-31 inches of mercury with divisions set at 1/20^th of an inch, annotated “Stormy,” “Rain,” “Change,” “Fair,” and “Very Dry,” and bearing the legend “Atmos – Barometer;” the inner raised on a single turned pillar with twin curved thermometers, at left a mercurial type, marked “Centigrade” and calibrated 0-40 degrees, at right a reddened spirit type, marked “Fahrenheit” and calibrated 30–110 degrees, the plate further marked “Atmos – Barometer” to top, “Made in France” to lower centre, “Brevete” to lower left, and “S.G.D.G,” to lower right – Brevete SGDG is a French non-government backed form of patent.

Heavy main chassis plate, the principal lever of L-shaped form raised on twin turned pillars with knife-edge pivots and bearing upon a single steel coil spring in compression raised on a turned pillar and seated on a threaded adjustment platform, the spur acting through short levers driving a grained, white metal indicator arm raised upon a turned pillar. The mechanism driven by twin 2½” capsules. Attractive grained and laquered brass telltale with short operator’s extension running in a nickeled escutcheon.

This piece is most probably the work of Jules Richard and is extremely well engineered and far superior in design and execution to most aneroid systems including those which followed it. Particularly noteworthy is the elimination of up to three sources of friction found in barographs and standard aneroid movements, which in turn contributes to a particularly sensitive and surprisingly accurate instrument. The movement is quite unlike any other mainstream instrument. Study of these movements has generally determined that coil spring tensioning produces a better balanced, more sensitive instrument – indeed the coil spring design endured for many years with different makers long after the C spring was introduced.

As in any delicate instrument, the setting up and testing is critical, and is often a laborious process. This Atmos Barometer has been painstakingly stripped and rebuilt, with particular attention paid to balance, and end float or “shake” in the critical moving parts (these invariably need attention as over time wear and damage leave the system in varying degrees of disarrangement). It has also been tested under laboratory conditions to establish the viability of the all-important pressure sensing capsules.

Overall in good condition, the movement as indicated working well with step-less progression. The movement, case and both thermometers are original, working and intact, the timber case sound with good colour.

A very attractive, much sought after instrument, this is certainly a collector’s piece, and a fascinating commentary on the development of the aneroid barometer. See Banfield, Edwin, “Barometers: Aneroid and Barographs,” p51 and p53, fig. 39 for description and image of a similar Atmos Barometer.