Submarine barometer having 8” silvered and machine engraved dial, the outer scale defined in inches of mercury with a range from 24 – 30.5. and divided to 20ths. The inner scale marked in millibars with a range from 820 – 1030 with divisions at 1Mb. The upper part marked “Compensated” and signed to the lower portion by the maker “Negretti & Zambra” with serial no. “17537.” Mechanical pointer stop set at 30.5 inches. Blued steel pointer, gilt brass telltale, bevelled glass.
Well-engineered lacquered and grey painted brass and steel movement driven by a single hardened steel 2½” capsule raised on three pillars. The whole contained within a heavily engineered brass and copper case, the verso with substantial mounting ring, compensation port.
We have recorded one other instrument of this type, no. 16559, which had been removed from Royal Navy submarine Affray. This instrument shares many of the characteristics of 16559 and although one thousand serial numbers later, is near identical in some respects. Of particular interest is the obviously heavy construction and the attention to rust proofing of the movement, together with the fitting of a bronze hair spring.
Most noteworthy, though, and a feature that both share, is the mechanical stop fitted to the dial at 30.5”. Unique to this type of barometer, this feature is designed to stop the movement from breaking at higher than design pressures. The fusee chain, a particularly delicate part of all these instruments, will be placed under significant tension, a primary cause of failure in these instruments generally caused by maladjustment.
It is very likely that the serial number range in which this instrument lies was also applied to other types of barometer – this would be consistent with information that we hold on other types of instruments. Thus, it would not be correct to assume that more than 1000 of this type were produced. Judging by the size of the submarine force the Royal Navy operated in the 1940s – some 60 boats – there would only have been a very modest number of these instruments built, perhaps around 500 over the course of the war.
The instrument shows signs of an original green painted finish, the dial re-silvered, some signs of dents to case having been lifted.
A very rare instrument, serviced and conserved, and offered here in full working order., in some respects,
Dimensions: 11″ diameter x 3½” deep
Stock No: BA0840