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Pascal's expedition. Engraving of the brother-in- law and two friends of the French physicist Blaise Pascal. They are carrying out an experiment in air pressure on the physicist's behalf. Pascal, who was also a mathematician and a philosopher, wanted to prove Torricel's prediction that air pressure would decrease with altitude. To do this a mercury barometer was carried to the summit of the Puy de Dome mountain, France (1200 metres high). The barometer recorded a drop in air pressure as the party made their ascent, thus proving Torricel's prediction.
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