CHAPTER II. PASCAL’S SCIENTIFIC DISCOVERIES.

of experiments with the view of verifying this explanation, and of banishing for ever the scholastic nonsense of Nature’s abhorrence of a vacuum. If the weight of the air was really the cause which sustained the height of the mercury in the Torricellian tube, he saw at once that this height would vary at different elevations, according to the varying degree of atmospheric pressure at these elevations. He proceeded accordingly to test the result; but the higher levels around Rouen were too insignificant to enable him to draw any decisive inference. Accordingly, he communicated with his brother-in-law in Auvergne with the view of having an adequate experiment made during an ascent of the Puy de Dôme, which rises in the neighbourhood of Clermont to a height of about 3000 feet. The state of his own health prevented him from conducting the experiment personally, and M. Périer was detained by professional avocations from undertaking it immediately. But at length, in September 1648, the experiment was carried out successfully, and the results communicated to Pascal. I cannot do better than quote the account of this important event as rendered by an eminent scientific authority,⁸ from M. Périer’s own recital of the facts in his letter to Pascal:—