Various ways of further testing the evident inferences to be drawn from this beautiful experiment, were so obvious, that it is impossible to suppose the illustrious philosopher to whom we are indebted for it, would not have pursued the inquiry further, had not death, almost immediately after this, prematurely removed him. The experiment became known, and excited much interest in every part of Europe; and Mersenne, who had an extensive scientific correspondence, having received an account of Torricelli's investigation, communicated the particulars to Pascal. Always reluctant to surrender long established maxims, the philosophers of that day rejected the solution of the problem given by Torricelli, and still clung to the maxim that "nature abhors a vacuum." The sagacity of Pascal, however, could not be so enslaved by received notions; and he accordingly, assisted by M. Petit, applied himself to the discovery of some experimental test, of a nature so unanswerable as to set the question at rest. The result was the celebrated experiment on the Puy de Dôme, the first and most beautiful example of an "experimentum crucis" recorded in the history of physics. Pascal argued, that if the weight of the incumbent atmosphere were the real agent which sustained the mercury in Torricelli's tube, as it was inferred to be by that philosopher, any thing which would diminish that weight, ought to diminish in the same proportion the height of the mercurial column. To test this, he first conceived the idea of producing over the surface of the mercury in the cistern in which the end of the tube was immersed, a partial vacuum, so as to diminish the pressure of the air upon it. But, apprehending that this experiment would hardly he sufficiently glaring to overcome the prejudices of the scientific world, he proposed to carry the tube containing the mercurial column upwards in the atmosphere, so as gradually to leave more and more of the incumbent weight below it, and to ascertain whether the diminution of the column would be equal to the weight of the air which it had surmounted. No sufficient height being attainable in Paris, the experiment was conducted, under Pascal's direction, by his brother-in-law, M. Périer, at Clermont, on the Puy de Dôme, a hill of considerable height, near that place. The experiment was completely successful. The mercurial column gradually fell until the tube arrived at the summit, and as gradually rose again in descending. Bigotry and prejudice could not withstand the force of this, and immediately gave way. The maxim of nature's abhorrence of a vacuum was henceforth expunged from the code of natural science; and, what was still more conducive to the advancement of all true science, philosophers were taught how much more potent agents of discovery, observation and experiment, guided by reason, are, than the vain speculations in which the ancients had indulged, and from the baneful influence of which scientific inquirers had not yet been