A good early British Military issue aneroid barometer altimeter No 851 by F. Darton & Co, London c1890

Aneroid barometer altimeter having 4¼” silvered and die struck dial, outer scale calibrated in feet with a range from 0 – 7,000ft and divided down to 10ft, inner barometric scale calibrated in inches Hg with a range from 24” – 31” and divided to 1/100ths”, the upper part marked “Compensated” with serial “No 851,” the lower part signed by the maker “F. Darton & Co, London.” Fine blued steel pointer set beneath a bevelled glass, held in a rotating bezel with index. Conventional high quality movement driven from a 2¾” nickel alloy capsule tensioned on a C spring.

The whole contained within a brass military pattern drum form case, mounting block with heavy pinned and double articulating suspension ring.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions. The movement working well over full service deflection, see performance chart. The dial probably lacquered, generally clean with very minor marks to centre. The case patinated overall, minor abrasions and signs of wear.

Comments: A military contract probably for the engineers, very useful in construction. The levels of accuracy attainable with this instrument might have made it suitable for gun laying, barometric pressure a significant variable in ballistic calculation.

Not desperately uncommon however this is an early version of this instrument – not only is the instrument number 851 relatively early, but the capsule is the early circumferentially soldered seam type.

A much above average and original example of a really very overlooked instrument for both its historical and quality significance.

Banfield, Edwin, Barometer Makers and Retailers, 1660-1900 records Francis Darton & Co as working from various addresses in London from 1834 onwards, and the company existed up until the 1990s.