A very good scarce five glass lacquered brass recording barometer or barograph No 1409 by Naudet c1905

Barograph constructed principally in lacquered brass, the movement driven from a seven autonomous cell pressure sensor tensioned on a bright plated C spring. The primary spindle and bridge assembly supported on twin A frames with calibration adjustment wheel. The primary lever with adjustable counter weight and bimetallic temperature compensation. Drop link to secondary lever with fine keyed gain adjustment, secondary spindle with fine spring steel recording arm.

The assembly raised over a heavy plate chassis on turned pillars, the crossbeam marked “Barometre Holosterique.” Standard 3½” diameter recording drum with paper clip, captive key and spigot location, securing nut. The sun wheel struck “103.” Chassis mounted thermometer set on silvered register calibrated in degrees centigrade. Arrestor bar with base mounted lever. Lift off lid glazed with five deep bevelled glasses. The chassis carrying serial no. “1409” and stamped with the Naudet “PHNB” logogram.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions, see performance chart from dynamic test. The instrument working exceptionally well with good sensitivity and near perfect accuracy across the range 28 – 31” Hg. The thermometer with unbroken thread and accurate to within ½° at 25°.

The chassis re-lacquered, the lower plinth and lift off lid with much original finish, three glasses replaced due to chips. The clockwork serviced and working well.

Comments: Instruments of this pattern are rarely seen. This is a study in real excellence in engineering as not only is the design and execution as good as any instrument of this type from the period, but the attention to detail far surpasses anything else.

Perhaps the most obvious feature of this instrument is the arrangement of the pressure sensing cells and the inclusion of a C type – or as Naudet describes it, a swans neck type – spring as the tensioner. In the vast majority of barographs with cells like these, the cells are internally sprung. This design utilises just one spring tensioning all the vertically connected cells equally. This gives several advantages: firstly, there is much better predictability or consistency over the pressure cycle; secondly, the extension (under lower pressures) or compression (higher pressures) maintains a better concentricity in vertical movement of the cells; thirdly, the effects of thermal expansion become more predictable.

To underscore this important development in design, substantial A frame supports are located on either side, increasing the rigidity of the sensor cell unit and contributing to a more faithful transmission of the smaller pressure fluctuations.

The inclusion of bimetallic compensation, a counterweight, and micro adjustment to gain are all features not seen together on other contemporary instruments. Although undeniably attractive, this is much more than just a domestic barograph – this was a masterpiece for which there were no comparables.

A delight to the eye. A study in engineering excellence. A masterpiece of innovation.

NB: The image of the catalogue page is taken from the Naudet Dourde Baromètres Holostériques catalogue of 1928 (courtesy of analogweather.com). Below the image of the brass barograph at the bottom is a comment referring to a note on the next page:

Information for Compensated Recording Barometers
The recording barometer (barograph) we have been building since 1900 has, thanks to the advantages derived from the principles underlying its design, earned a reputation equal to that of the ordinary barometers the company has been making since 1860. Its principle, based on the use of a curved spring in the shape of a swan’s neck holding apart the walls of a stack of vacuum boxes stacked on top of each other to balance atmospheric pressure, gives it an undeniable superiority.

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