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Lot Essay
COMPARATIVE LITERATURE:
E. Banfield, Barometer Makers and Retailers, Trowbridge, 1991
N. Goodison, English Barometers and Their Makers 1680-1860, Woodbridge, 1977
At the age of 21 Peter Dollond set up as an optician in Vine Street, Spitalfields. He later went on to become one of the most eminent optical instrument makers of the late 18th Century and was appointed optician to King George III and the Duke of York. Among his workers was Jesse Ramsden who was said to make scales for Dollond and who in 1766 became his brother-in-law. In 1799 Dollond became Master of the Spectacle-makers Company.
Atmospheric pressure is measured by the height of the mercury column above the surface of the mercury in the cistern. As the barometer scales are fixed, the level of the mercury in the cistern needs to be zeroed before an accurate reading can be taken. The method commonly used on domestic barometers is attributed to Ramsden and incorporates a float resting on the surface of the mercury and connected to an ivory gauge screwed into the cistern. The lower cistern screw is turned to adjust the height of the mercury to the neutral point from which the register plates were calculated. When this point has been reached a correct reading can be taken.
E. Banfield, Barometer Makers and Retailers, Trowbridge, 1991
N. Goodison, English Barometers and Their Makers 1680-1860, Woodbridge, 1977
At the age of 21 Peter Dollond set up as an optician in Vine Street, Spitalfields. He later went on to become one of the most eminent optical instrument makers of the late 18th Century and was appointed optician to King George III and the Duke of York. Among his workers was Jesse Ramsden who was said to make scales for Dollond and who in 1766 became his brother-in-law. In 1799 Dollond became Master of the Spectacle-makers Company.
Atmospheric pressure is measured by the height of the mercury column above the surface of the mercury in the cistern. As the barometer scales are fixed, the level of the mercury in the cistern needs to be zeroed before an accurate reading can be taken. The method commonly used on domestic barometers is attributed to Ramsden and incorporates a float resting on the surface of the mercury and connected to an ivory gauge screwed into the cistern. The lower cistern screw is turned to adjust the height of the mercury to the neutral point from which the register plates were calculated. When this point has been reached a correct reading can be taken.