Pascal and Perrier.

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Chap. 2.\

was Pascal, a French mathematician and divine. In 1646 he undertookto verify the experiments of Torricelli , and still fnrther to Vary them.He used tubes of glass forty feet long, having one end closed to avoidthe use of a syringe. He filled one with wine and another with water, andinverted them into basins containing the same liquids, after the manner ofTorricelli ’s mercurial experiment. As the specific gravity of these liquidswas not the same, he anticipated a difference in the length of the two co-lumns; and such was the fact. The water remained suspended at theheight of thirty-one feet one inch and four lines; while the lighter winestood at thirty-three feet three inches. Pascal was attacked with greatvirulence by Father Noel, a Parisian jesuit, who resisted the new doctrinewith infuriate zeal, as if it also was heresy, like Galileo’s doctrine of theearth’s motion round the sun.

After making several experiments, one at length occured to Pascal,which he foresaw would, if successful, effectually silence all objectors.He reasoned thus : If it is really the weight or pressure of the atmosphere,that sustains water in pumps, and mercury in the tube, then, the intensityof this pressure will be less on the top of a mountain than at its foot, be-cause there is a less portion of air over its summit than over its base ; iftherefore a column of mercury is sustained at 28 or any other number ofinches at the base of a very high mountain, this column ought to diminishgradually as the tube is carried up to the top; whereas, if the atmospherehas no connection with the ascent of liquids, (as contended) then the mer-cury will remain the same at all elevations, at the base as at the summit.Being at Paris , he addressed a letter to his brother-in-law, M. Perrier,(in 1647) from which the following is an extract: “ I have thought of anexperiment, which, if it can be executed with accuracy, will alone be suf-ficient to elucidate this subject. It is to repeat the Torricellian experi-ment several times in the same day, with the same tube, and thesame mercury ; sometimes at the foot, sometimes at the summit ofa mountain five or six hundred fathoms in height. By this meanswe shall ascertain whether the mercury in the tube will be at thesame or a different height at each of these stations. You perceive with-out doubt that this experiment is decisive ; for if the column of mercurybe lower at the top of the hill than at the base, as I think it will, it clear-ly shows that the pressure of the air is the sole cause of the Suspensionof the mercury in the tube, and not the horror of a vacuum; as it is evi-dent there is a longer column of air at the bottom of the hill than at thetop; but it would be absurd to suppose that nature abhors a vacuummore at the base than at the summit of a hill. For if the Suspension ofthe mercury in the tube is owing to the pressure of the air, it is plain itmust be equal to a column of air, whose diameter is the same- withthat of the mercurial column, and whose height is equal to that of theatmosphere, from the surface of the mercury in the basin. Now the baseremaining the same, it is evident the pressure will be in proportion to theheight of the column, and that the higher the column of air is, the longerwill be the column of mercury that will be sustained.” This experimen-tumerucis, was made on the 19th September, 1648, the year after Torri­ celli ’s death, on the Puy de Dome , near Clermont , the highest mountain inPrance ; and the result was just as Pascal had anticipated. The mercuryfeil in the tube as M. Perrier aseended with it up the mountain, and whenhe reached the summit it was three inches lower than when at the base.The experiment was repeated on different sides of the mountain, andcontinued by Perrier tili 1651, but always with the same results. Pas-cal made others on the top of some of the steeples in Paris ; and all