|A depiction of Blaise Pascal's 1648 atmospheric pressure experiment, wherein he had his brother-in-law Florin Perier carry a Torricelli barometer to the top of Puy de Dome, France, to see if the height of the mercury column would fall as a result of decreasing atmospheric pressure, as he predicted.
“I have thought of an experiment which will remove all doubt, if it be executed with exactness. The experiment should be made in vacuo several times, in one day, with the same quicksilver, at the bottom and at the top of the mountain of Puy, which is near our town of Clermont. If, as I anticipate, the height of the quicksilver be less at top than at the base, it will follow that the weight or pressure of the air is the cause of this; there certainly is more air to press at the foot of the mountain than at its summit, while one cannot say that nature abhors a vacuum in one place more than in another.”— Blaise Pascal (1648), “Letter to Florin Perier” (Ѻ)
“At eight o'clock, we met in the gardens of the Minim Fathers, which has the lowest elevation in town. First, I poured 16 pounds of quicksilver into a vessel, then took several glass tubes, each four feet long and hermetically sealed at one end and opened at the other. Then placed them in the vessel of quicksilver. I found the quicksilver stood at 26" and 31⁄2 lines above the quicksilver in the vessel. I repeated the experiment two more times while standing in the same spot. They produced the same result each time. Taking the other tube and a portion of the quicksilver, I walked to the top of Puy-de-Dôme, about 500 fathoms higher than the monastery, where upon experiment, and found that the quicksilver reached a height of only 23" and 2 lines. I repeated the experiment five times with care. Each at different points on the summit, found the same height of quicksilver, in each case.”