An important and rare transitional pattern aneroid “Mountain Barometer” altimeter by Negretti & Zambra c1863

Aneroid barometer having 2½” glazed and printed zinc-backed card dial, the barometric scale calibrated in inches of mercury with a range from 23” – 31” and divided down to 1/10th, inner altimetric scale calibrated in feet with a range from 0 – 8,000ft divided down to 100ft. The upper part marked “Mountain Barometer,” the lower with Registration Mark diamond indicating the year 1862. Early pattern blued steel pointer, bevelled glass, gilt brass index.

Standard miniaturised Vidi movement driven from a single 1¾” capsule tensioned on a C spring, bimetallic compensation, all contained within a spun drum-form case, calibration port to verso, together with inscription “Presented to Mr John Bisset by the 4th B.A.V. Corps as a mark of their high appreciation of his services as Secretary and Treasurer to the Corps since its formation, Portsoy, 23rd Novr 1863.”

Condition: The subject of a full service, conservation, and calibration under laboratory conditions. The movement working very well, see performance chart. The dial with minor ageing and very slight losses to printed parts, otherwise appearing clean and sharp. The glass without flaws, cracks or chips. The case retaining a good proportion of its original finish, some light wear, losses, and small patches of oxidation, light haze abrasion.

Comments: These early small instruments are really very rare, manufactured by Negretti & Zambra under the instructions of Admiral Fitzroy from 1860 onwards with a view to ultimately producing a truly pocket sized version, and it is thought that these mountain barometers were built over a period of only a couple of years or so. The construction is unique with the dial supported on a threaded ring enabling the precise dial height to be set – this arrangement was probably a way in which various experimental or pre-production movements could be fitted which may have differed in dimension.

The performance for an instrument now 160 years old is quite remarkable, allowing for the embrittlement of metals, and inevitable losses in pressure to the capsule – this is a testament to the excellence in the early making of these instruments. Over the years I have seen just two of these “mountain barometers” and two or three others of the same case pattern but dressed as standard barometers.

This is a very rare and important benchmark in the evolution of the aneroid barometer, and, it goes without saying, very collectable.

The 4th (Portsoy) Banffshire Artillery Volunteer Corps was formed on 8 October 1860.