Bourdon barometer having 5¼” white china clay finished hand decorated dial calibrated in inches of mercury with a range from 28 – 31 and divided to 1/100^th”, the centre with geo-concentric floral pattern, the upper part with standard meteorological terms, the lower part bearing the legend “The Compensing Metallic Barometer” with twin medallions for Gold Medal Exhibition 1849, cited as “E. Bourdon & Richard’s Patent, Paris,” and Universal Exhibition London 1851, cited as a “Council Award.” Fine blued steel pointer and skeletal gilt index with knob, retaining ring struck with serial no. “12074,” domed glass.

The early pattern movement constructed on a central beam with Bourdon tube, associated links, counterbalance and arbor mounted hairspring, the tube end marked “Compense,” the beam struck with Felix Richard logogram, “Compense,” “Richard à Paris,” “12074,” and inspectors marks “76J.” The tube mounting bracket struck “2 Serie, Bourdon & Richard, 12074”, and “Brevetes A Paris.” All contained within a spun and pressed drum form case flared at the mouth. Extension post and suspension ring.

Condition: This instrument has been the subject of a re-build, service, and calibration under laboratory conditions.The dial flat and clean, the markings crisp and clear, slight discolouration, ageing generally, minor marks and slight staining at lower periphery. The case clean and essentially damage free, generally worn, retaining traces of original finish.

The movement with some discolouration, points of oxidation, working exceptionally well with smooth responsive progression maximum error across the scale less than 0.05”. The glass with small flaw to centre, hard to pick up as this is set against dial decoration.

Comments: On the one hand the movement, unlike most Bourdon barometers, is not visible; on the other this is a very rare variation in exceptional condition.

The movement is of particular interest being essentially reversed from standard, the pointer fixed to a re-designed arbor, the pinion is of a larger diameter than standard, the rack remaining standard – this changes the gearing and may have a significant effect on response and resolution to the instrument’s benefit. Most Bourdon barometers with a range from 28” – 31” have a break between 28 and 31, this renders a dead zone – this instrument does not. A significant improvement allowing for a more open scale and thus higher resolution. It is exceptional for these instruments to retain this level of accuracy and with such an open scale.

The very attractive dial is also of interest as “The Compensing Metallic Barometer“ is a title that personally I have not seen before, and must be considered an extemely rare variation.

In all, this is a really lovely collectors Bourdon barometer, and its accuracy makes it good enough for a reference in a collection.