The mahogany veneered architectural frame with a broken-arch pediment, mounted with a silvered brass barometer register plate signed Polti, Exon to the top centre, the scale engraved 28 to 31 and sub-divided below into Stormy, Much Rain, Rain, Changeable, Fair, settled Fair and Very Dry. The circular hygrometer scale Dry/Moist mounted above the glazed aperture. The barometer tube running up the left and the thermometer, with silvered engraved brass scale, mounted to the right, each with a matching cylindrical cistern cover, the base also with a glass spirit level to the scooped centre.
The frame holding the original printed, semi-automated, Perpetual Regulation of Time calendar displaying a multitude of astronomical and calendrical information. Including days of the month, length of day, sunrise, sunset, fixed feasts, tides, moon phases and signs of the zodiac. It also gives the dates of Easter from 1753 to 1852. While the hygrometer is moved using conventional brass wheels, the series of movable paper dials are mounted onto wooden wheels through the back and set by brass turns, with cords, operating through the frame.
As far as we are aware this is the only surviving perpetual calendar barometer by Charles Polti; indeed, it appears to be the only provincial example known of this type.
Charles Polti, Exeter circa 1770
An exceedingly rare and possibly unique, provincial mahogany framed, perpetual calendar with mercury angle-tube barometer, thermometer, hygrometer and level.
Charles Polti (circa 1765-1790)
Charles Polti was a highly accomplished but little-known barometer and scientific instrument maker from the city of Exeter in Devon. An unusual inverted wheel barometer is illustrated in Barometers, wheel or banjo, the barometer is solid mahogany with highly elaborate foliate carving to the tube and cistern covers. There are fewer than 15 perpetual calendar barometers recorded, all the others are by London makers, mostly made by Watkins and, later, Watkins & Smith with no fewer than five in The Gerstenfeld Collection of Washington, DC, however another reference is mentioned in English Barometers and their Markers, where Goodison describes a yew-wood barometer of the form as the present example, also by Polti, but with a mirrored centre rather than a complicated perpetual calendar.