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Air pressure experiment. Illustration of Florin Perier in September 1648, on the request of his brother-in-law French physicist Blaise Pascal, measuring the air pressure as he ascends the Puy de Dome volcanic mountain in France (elevation: 1464 metres). He is using an early barometer invented by the Italian physicist Evangelista Torricelli in 1643. The column of mercury in the sealed glass tube fell in height during the ascent. This proved that air has weight.
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