Silver Pocket Barometer with Thermometer by Thornhill c1899

A very good scarce silver cased pocket barometer with thermometer by Thornhill c1899 bearing a viscount's coronet. Pocket barometer having 1¾" silvered and engraved stepped dial with outer bezel-activated altitude ring, having a range from 0 – 8000ft, inner barometric scale calibrated in inches of mercury with a range from 23" – 31", inset dial with semi-circular thermometer calibrated in degrees Fahrenheit with a range from 30 – 130, the upper part marked with meteorological terms "Rain, Change, Fair." Blued steel pointer, all set beneath a bevelled glass. The 1" capsule driven conventional movement tensioned on a C type spring, all contained within a drum form lacquered brass case. The movement, dated "10/99", unsigned but undoubtedly by Negretti & Zambra. The whole fitted into fine quality English silver case having hallmarks to inner lid and case verso also having calibration port and inscribed "Thornhill, Bond Street, London." The silver case with minor marks having good polish and colour, slight depression to lid.  The hinge with slight play though sound. The dial crisp and vibrant, the barometer movement performing well with good progression. The subject of a thorough overhaul, the movement dismantled serviced and re-calibrated. Comprehensively tested under laboratory conditions, good performance was noted within the normal barometric range, see performance chart below. Expected errors > 10% were noted at the lowest pressures - this is entirely normal. Hysterisis as tested over five minutes was noted as within normal limits. Overall performance to full scale deflection must be noted as well above average. The silver case would have been lined with reasonably compliant material in order that the barometer remained secure but might if required be withdrawn. This material was lacking so here a combination of heavy green baize backed with leather has been fitted and this might well have been very much as the original making. Our research suggests that there were two possible owners in 1899 for this silver pocket barometer, both within the same family. The first, James Gascoyne-Cecil, Viscount Cranborne, was the eldest son of the three-times Prime Minister Lord Salisbury, the second, his younger brother Robert Cecil, 1st Viscount Cecil of Chelwood. A lovely object, and clearly of good enough quality for a senior member of the aristocracy. Very much a collector’s piece.