A RARE GEORGE IV PORTABLE MERCURY STICK 'MOUNTAIN' BAROMETERTHOMAS RUBERGALL, LONDON, CICA 1825Of cylindrical form with silvered scroll-engraved break-arch crest over elongated scale calibrated in barometric inches ranging from 23.3 inches to 32 inches, with the ual weather observations and signed Tho's Rubergall, Coventry St. LONDON to lower left hand margin, the waist with brass collar fitted with knife-edge pivots for mounting within the gimbals and curved silvered scale mercury tube Fahrenheit scale thermometer to shaft, the base terminating with a brass sleeve incorporating level adjtment screw inside a threaded cap to base, the instrument mounted via pivoted gimbals onto a tripod with brass caps and spike feet which also closes to create a cylinder inside which the barometer is transported.The instrument 91.5cm (36ins) high, the tripod 6.5cm (2.5ins) diameter.Provenance: The archive collection of Barometer World Meum, Merton, Devon.Thomas Rubergall is recorded in Clifton, Gloria Directory of British Scientific Instrument Makers 1550-1851 as working in London 1800-54, most notably from several addresses in Coventry Street from 1805. He was optician and mathematical instrument maker to the Duke of Clarence and optician to King George III.True portable 'mountain' barometers were ed to assist with calculating altitude by observing the drop in the mercury column whilst ascending a topographical feature. Mercury mountain barometers are now very rare due to their low survival rate which is probably mostly a consequence of them bing redundant with the introduction of the aneroid barometer during the middle of the 19th century.