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Pascal's expedition. Coloured 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 wanted to prove Torricelli'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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