An interesting lacquered brass early wrist air altimeter by Negretti & Zambra, London no. 3257 with provenance to Ralph Whitehead. R.N.A.S., c1914

Wrist air altimeter having 3” silvered and engraved dial, the outer bezel setting altitude ring marked “Feet” and calibrated in feet with a range from 0 – 7,000ft divided down to 50ft, inner barometric scale in red, calibrated in inches of mercury with a range from 24” – 31” and divided down to 1/10”, the upper part marked “Compensated,” the lower signed by the maker “Negretti & Zambra, London” with serial no. “3257” and N&Z logogram. Blued steel pointer, bevelled glass.

Conventional 1st quality gilt finished movement driven from a single special 1½” capsule tensioned on a C spring, the bridge dated “1/13” (January 1913), the whole contained within a rolled and turned brass case, strap guides to sides, the verso machine engraved “Ralph Whitehead R.N., Royal Naval Air Service, 1914.” Calibration port.

Presented in its original burgundy leather over timber, green velvet and silk lined case, gold block cartouche to lid silk with maker’s London address, cut outs for strap lugs and bars, snap closure on a button release.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions, see performance chart from dynamic test. The movement working well with excellent sensitivity and very acceptable accuracy across the range.

The dial very clean, the lacquered brass case with minor marks and signs of wear and points of slight oxidation. The travel case in excellent condition.

Comments: This altimeter was included in the Negretti & Zambra catalogue c1915 (item 275) and mentioned in N&Z’s advert in Aeronautics magazine of June 1913, see images.

It is very unusual for an altimeter from this or for that matter any other period to be accompanied by irrefutable provenance.

Ralph Whitehead – TBC

As for the instrument, this is an interesting study compared alongside its counterpart no. 3266, delivered to the Central Flying School, and also housed within the Vavasseur Archive. The two are, of course, constructed in different metals, 3257 in brass and 3266 in aluminium, but share a number of common characteristics. Dimensionally they are very similar though not quite identical.

Engineering differences are evident since aluminium may not be easily soldered and so the movement fixings and strap lugs are secured in the aluminium version with machine screws threaded into the aluminium body, whereas in the brass version these have been soldered.

One aspect that does stand out is that both have hand-engraved altitude rings suggesting very low production of instruments of this type.

In all, this is a unique and most important instrument as a commentary on instrument making and flying of the period.