A very unusual, possibly commission, aluminium Surveying and Mining Aneroid no 8911 with vernier and setting altitude scales by Negretti & Zambra c1915

Aneroid barometer having 4¼” silvered and die struck engine divided stepped dial with wheel driven outer vernier marked “Ascent” and “Descent” and 0 – 10, middle altimetric scale calibrated in feet with a range from 0 – 4,000ft and divided down to 10ft, inner barometric scale calibrated in inches of mercury with a range from 27″ – 33″ divided down to 1/50th. The upper centre marked with “Ascent” and “Descent” arrows, “Surveying and Mining Aneroid” and “Compensated,” the lower part signed by the maker “Negretti & Zambra, London” with serial no. “8911.”

The finely set and executed  Vidie pattern  movement  mainly constructed in frosted gilt finished brass raised over an iron chassis and driven from a single 2⅝” nickel alloy capsule of soldered construction tensioned on a C Spring. Affixed with spacers and machine screws with low dome heads.

All contained within a cast and spun drum form aluminium case, twin side mounted setting wheels for altitude and vernier, revolving and extending dial loupe, calibration port to verso.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions, see performance chart from dynamic test. The movement exhibiting high levels of accuracy, sensitivity and stepless progression.

Received in very original ‘as found condition,’ the aluminium case cleaned, re-grained and re-lacquered, the dial with slight ageing and minor marks otherwise crisp, minor marks to glass. Both vernier and altitude setting scales move smoothly with ideal resistance, the loupe clear without damage, rotating and extending smoothly.

Comments: Although the Negretti & Zambra catalogue of 1915 lists both a “Surveying” and a “Mining” aneroid barometer, the latter with the same range as this instrument, we have been unable to verify any similar examples with twin setting wheels. It must therefore be concluded that either this was a one off commission piece for special application or production of extremely limited volume. The precision and relative complexity in producing this instrument immediately set it aside from the vast bulk of competing survey types.

Under observation for some time the movement is capable of resolving changing values not only with great precision but without steps, a characteristic that might have been more commonplace in new instruments of the time but one which is rarely encountered now. The movement is a study in fine making, clearly reflected in its performance. A remarkable instrument, the mechanical attributes of which suggest resolution to 1″.

Interestingly, from a design and production engineering point of view, it shares much in common with a small number of very specialised “Maximum Height Recorders” for aircraft, principally made for Short Brothers at this time.

Representing the finest in making of the period this is an evidentially superb piece of engineering working to very close tolerance.