A pair of near identical aneroid aluminium pocket barometer altimeters, 2” silvered dual concentric engraved dials with rotatable altitude scales. No. 762, the inner calibrated in inches/Hg with a range of 25–31 inches of mercury, the outer with an altitude range from 0-8,000ft. No. 812, the inner calibrated in cm/Hg with a range 59–79 cm of mercury, the outer with an altitude range of 0–2500 metres. The dial centres marked “Compensated,” signed by the maker “Ross, London,” serially numbered “762” and “812.” Fine blued-steel pointers set beneath bevelled glass. Machined high polished bezels set to flat finished cases, stems with suspension loops. High quality lacquered brass conventional movements with bimetallic compensation to secondary levers. The case rears with twin alloy dome-headed machine screws, compensation ports set at 4 o’clock. Presented in their original, fine, burgundy, embossed patent Moroccan leather-covered cases with cream silk and imperial purple velvet linings, the cases retaining virtually all their original finish.

These barometric altimeters are not only very similar in construction and age, but manufactured in the same material, aluminium – a material that attracted a premium price and was generally only supplied by special order. They are most complementary by virtue of metric and imperial value. In the absence of any compelling provenance, we present them here as a composed pair, i.e. collected from different sources.  However, we acquired them together and, since they are both extremely scarce and very close to each other by serial number and in condition, it is reasonable to suggest that they were originally purchased as a pair.

The specification for aluminium strongly suggests either an aviation or scientific exploration application. The movements of alloy-cased instruments can only be practicably fixed into the cases with machine screws, the heads of which are almost always visible to the rear (movements were fitted to brass-cased instruments with fine-threaded bolts soldered to the inside of the case). No 812, the metric altimeter, is in extremely fine condition with little sign of use. No 762, the imperial altimeter, shows some signs of use with very minor wear only. The same applies respectively to the original leather cases.

As a pair, these pocket barometers afford a fascinating study in the manufacture of these rare instruments. Serviced, calibrated, in good working order and in near-new condition.

Dimensions: 2½” diameter x 1¼” deep

Stock No: PB0328/9

Price: Vavasseur Archive