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Torricelli, Evangelista

mercury column weight pressure

[tori che lee] (1608–47) Italian physicist: inventor of the mercury barometer and discoverer of atmospheric pressure.

An orphan, Torricelli was educated by the Jesuits and by B Castelli (1578–1643), for whom he worked on the dynamics of falling bodies. This led to his being appointed assistant to , whom he subsequently succeeded as mathematician to the court of Tuscany.

Torricelli’s interests covered pure mathematics and experimental physics; he worked on conic sections and other curves, deriving the area of the cycloid. He is best remembered, however, for his discovery of atmospheric pressure and for his invention, in 1643, of the mercury barometer. This appears to have come about from an attempt to solve the problem of why water could not be pumped out of a well more than 33 feet (˜ 10 m) deep. Deducing that the reason was that the atmosphere possessed weight and therefore exerted a pressure, he set about verifying the idea by sealing a glass tube at one end, filling it with mercury and inverting it with the open end in a dish of mercury. He found that the height of the mercury column fell to about 760 mm, and reasoned that a vacuum was formed above it; the weight of the column was being balanced by the weight of the atmosphere. He later noticed the small daily variations in the height of the column, which he related to changes in the weather.

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