An extremely rare, very important and early, aluminium aviation altimeter by Negretti & Zambra, c1911, designed for the Central Flying School of the Royal Flying Corps

Aircraft altimeter having silvered brass 5¼” dual concentric dials, the inner calibrated with a range 28-31 inches of mercury, further annotated “Compensated,” “Inches,” and with maker’s legend “Negretti & Zambra, London.” The outer rotating dial annotated in feet, boldly marked in one hundreds of feet with stations at 1, 2 and 3000ft. Broad blued-steel pointer set beneath a fine ground, optical quality bevelled glass, the bezel with fine cut knurling to circumference. The two-inch deep parallel cast and machined case with side-mounted bracket and bezel stop. First quality twin 2½” diameter capsule movement having bi-metallic compensation and constructed upon an aluminium chassis. The whole retained within its original leather case by three aluminum fixing screws to rear. The leather case lacking fixing points, and with plaited leather cord with copper fixings (later). The aluminium instrument case with some surface oxidation and minor abrasions, the glass with minor scratches, the dial with some localised oxidation.

The leather case originally had four circumferentially-spaced leather fixing tabs with hard eyes. At some point they have been removed, but they would have been pick up points for mounting wires or springs, a system of suspension within the framework of the aircraft and designed to position the instrument for easy viewing by the pilot and to reduce vibration generated by the engine. The bezel may be rotated and locked into position setting the Zero marker at the pointer prior to take off, thus giving an accurate altitude over field height.

Since numbers of aircraft at this time were minimal, production of these early aviation altimeters would have been very few indeed. This highly significant aneroid aviators altimeter was designed for the Central Flying School, Upavon, which was set up to train service pilots when the Royal Flying Corps was created in 1912. (Source: Imperial War Museum). The instrument is of identical pattern to one found in the Aeronautics collection of the Science Museum (object no: 1927-323) which is marked ‘Central Flying School No II” and dated c1914, and which carries a greater full-scale deflection to 7000ft. This information is extremely important since the altimeter offered here may be an example of the earliest collaboration between the British Government and any manufacturer to develop these instruments.

An image of this aircraft altimeter also featured in a Negretti & Zambra advertisement in Aeronautics magazine in June 1913, though the instrument shown there is scaled to 5000ft.

This Negretti & Zambra aviators altimeter was obtained by us in essentially untouched condition. It has been disassembled, checked, cleaned, conserved and reassembled. It is in absolutely original condition and its function and sensitivity are excellent.

Despite exhaustive enquiries, we have been unable to find any examples that pre-date this instrument, making this probably the earliest known dedicated aircraft altimeter of this type. It represents a moment in time when technology, engineering and science, married to the great pioneers in aviation, forever changed the world.

Negretti & Zambra, founded in 1850 as makers of scientific instruments, were the most prolific and leading makers of all types of barometers during the second half of the 19th century and into the 20th century.

The partnership exhibited at the Great Exhibition at the Crystal Palace in 1851 and won a Prize Medal. Negretti & Zambra held the appointment of instrument-makers to Her Majesty Queen Victoria, Prince Albert and Edward VII, the Royal Observatory and the British Admiralty (see Banfield, Edwin, “Barometer Makers and Retailers, 1660-1900”).