A rare mining aneroid barometer designed and constructed by Negretti & Zambra having 8″ painted and engraved dial with a barometric range of 27 – 33 inches of mercury, the upper portion marked “Mining Aneroid,” the lower portion signed by the retailer “John Davis & Son (Derby) Ltd,” and carrying a curved thermometer, the register calibrated in degrees Fahrenheit with a range 20 – 140. Blued steel pointer and gilt brass telltale under bevelled glass retained by polished brass bezel. Conventional 1st quality 2½” capsule-driven C-spring tensioned movement with bronze hairspring and bimetallic compensation. The whole raised on three columns within a low spun drum form copper case, verso with fixing points, compensation screw port at 4 o’clock.
Overall condition is excellent though it should be noted that the case would originally have been japanned, the finish having been removed at some time to reveal the aesthetically pleasing copper and brass. Some discolouration to the dial, case remarkably dent-free, movement having been fully serviced and calibrated – see performance chart below in which it will be noted the accuracy is more than acceptably good.
This instrument was made by Negretti & Zambra to a basic design that was also fitted to submarines, and offers a scale reading, unusually, up to 33″ Hg (most barometers read to 31″ Hg).
Colliery, Mining or Pit Barometers were made specifically for use in mines from early in the 19th century, with a higher reading scale than above ground barometers. In 1872, an Act of Parliament was passed making their use compulsory. Records clearly showed that before an explosion in a coal mine there had been a diminution of atmospheric pressure, enabling flammable gasses trapped in rock strata to more readily flow into the open spaces in a mine. The Act required a barometer to be placed above ground in a conspicuous position near the mine entrance but they were always made of solid construction so they could also be used underground, as an indicator to when circumstances could be declared particularly dangerous. With the scale going up to 33″ the barometer could be used at least 2,000 feet below sea level.
A rare, very attractive and functional instrument.
Dimensions: 9½” diameter x 2¾” deep
Stock No: BA1320