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tributions to physical science, which afford still more remarkable proofs of the premature vigor of his intellect. His celebrated experiments upon the weight of the atmosphere put the seal of demonstration upon one of the greatest discoveries of modern times. Torricelli suspected that the ascent of water in a common pump, which had hitherto been attributed to nature's repugnance to a vacuum, was really due to the weight of a column of air, which balanced the column of fluid. The workmen of the Duke of Florence bad informed him, that the pump would not act for a height of more than thirty-three feet. If the weight of the atmosphere, then, would support a column of water thirty-three feet high, it would balance a much heavier Auid only at a much lower elevation. Torricelli took a glass tube about three feet long, sealed at one end, and having filled it with quicksilver, he plunged the open end into a cup full of the same Auid, and found that the mercury in the tube, after some oscillations, remained at the height of about thirty inches above the surface of the mercury in the cup. Mercury is about thirteen times heavier than water, and thirty inches is about the thirteenth part of thirty-three feet. In other words, the power which supported the two Auids, whatever it might be, was constant in respect to weight, since the elevation of the two fluids was inversely proportional to their weight. Torricelli believed, that this power was the pressure of the air, or that a column of air as high as the earth's atmosphere was as heavy as thirty inches of mercury, or as thirty-three feet of water. But he could not prove this ; his supposition, it is true, explained the facts ; but it did not exclude other hypotheses which might be framed to account for the same phenomena. The question remained open, then, till, in the language of Bacon, an experimentum crucis could be devised, which should eliminate the false theories, and show that the weight of the atmosphere was the only possible cause of the phenomenon. This experiment was at last devised and executed by Pascal, who thereby put the question for ever at rest.

The experiment of Torricelli, which was, in truth, the invention of the barometer, was made in 1645. Its result had been predicted by Descartes ; but the explanation offered by both these philosophers had at first but small success among the learned. The doctrine of the repugnance of nature to a vacuum had been too long established to give way readily to a truth which was not as yet demonstrated. The supposition was gravely made, that some subtile matter, or ether, evaporated from the surface of the water or the mercury, and filled the apparent void in the top of the tube. Pascal at once adopted the views of Torricelli and Descartes, and repeated the experiments of the former in 1646, with some variations, which still further discredited the old doctrine. He used tubes of great length, and thus proved that nature did not dread a great vacuum any more than a small one. He employed a tube bent in the form of the letter U, and having invented an apparatus for adınitting at intervals small quantities of air into the top of one of the branches, he found that the mercury descended there just as fast as the air was admitted, while it remained stationary in the other branch. The results of these experiments, and the arguments founded upon them, he published in 1647, in a little book, entitled “New Experiments respecting a Vacuum.” Noel, a Jesuit, who was then rector of the College of Paris, published a severe criticism upon this work, and Pascal replied in a sarcastic and argumentative way, showing the power in controversy which was afterwards more fully developed in the “ Provincial Letters."

But Pascal saw with pain, that not one of the tests or arguments hitherto employed was absolutely decisive of the point at issue. After long and painful reflection upon the subject, he at last matured the idea of an experiment, which would leave no room for cavil, and would establish the true doctrine irrevocably. If the air be a weighty fluid, each horizontal stratum of it must be pressed by the accumulated weight of all the superincumbent strata, and the pressure must therefore diminish as we rise above the surface of the earth. Now, if it be the pressure of the air which sustains the column of Auid, let the instrument be carried to a considerable height in the atmosphere, and the mercury must fall to a lower point in the tube. In order that the difference in the height of the mercury might be very perceptible, and leave no pretext to doubt its reality, it was necessary to raise the tube very high in the air. The mountain called the Puy-de-Dôme, which is in the neighbourhood of Clermont, and is about three thousand feet high, offered a suitable means for accomplishing this object. On the 15th of November, 1647, Pascal communicated his project to his brother-in-law, M. Perier, who was about to visit Clermont, and charged him to make the trial as soon as he arrived there. Various circumstances delayed the execution of the plan ; but it was tried at last, with all possible exactness, on the 19th of September, 1648, and all the phenomena were observed which Pascal had predicted. The mercury began to descend in the tube as they climbed the mountain's side, and on the summit it was more than three inches lower than it had been at the base. As they descended, the column rose again, till they reached the plain, where it had the same elevation as at first. In another tube, which had been observed meanwhile on the plain, no alteration had taken place. Pascal made similar experiments at Paris, by means of the very lofty tower of St. Jacques-la-Boucherie, and obtained corresponding results.

Herschel, quoted with approbation by Mr. Hallam, calls this famous experiment "a crucial instance, one of the first, is not the very first, on record in physics.” Indeed, the whole history of Pascal's investigations respecting the pressure of the atmosphere is such a striking and beautiful illustration of the Baconian system, that we must believe he had studied the “Novum Organum," an edition of which was printed in Holland in 1645, just a year before Pascal began his work. His final success appears the more remarkable, when we consider that he was not yet twenty-five years old. Descartes, with his usual selfishness and arrogance, claimed the merit of this experiment for himself, by affirming, in a letter written in 1649, that he had suggested it to Pascal two years before. This assertion was communicated to the latter, who disdained to take any direct notice of it ; but in a historical account of the matter, which he wrote in 1651, he says, without mentioning Descartes, “I boldly declare that this experiment is of my own invention ; and I say, moreover, that the increase of knowledge which it has occasioned is due entirely to me.” If we reflect on the severe integrity of Pascal's conduct, the rigid conscientiousness which

pervaded his character, and the frank and manly way in which he acknowledges the merit due to others, evinced particularly by his language respecting Torricelli, it seems impossible to discredit this distinct assertion. “The question is one of those," says Playfair, “ where a man's conduct in a

particular case can only be rightly interpreted from his general character and behaviour.” It is notorious, that Descartes was far from being frank and candid in his intercourse with others. He contrives to give a history of the origin of the telescope without mentioning Galileo ; he says nothing of the discoveries of Kepler, though so nearly connected with his own; and his conduct towards Snellius subjects his integrity to the heaviest imputations. “The truth is,”

says Playfair, “ that he appears throughout a jealous and suspicious man, always inclined to depress or conceal the merit of others.” Surely, when a question of veracity arises between two such persons as Pascal and Descartes, we cannot doubt for a moment which is to be believed.

The experiments upon the pressure of the atmosphere naturally led Pascal to some more general inquiries respecting the equilibrium of Auids. He wrote two treatises upon this subject and upon the weight of the air, which were finished in 1653, though they were not published till after his death. They contain the record of some ingenious experiments, and many general views, which were considerably in advance of the science of his time. He remarks, that the air is a compressible and elastic fluid, and cites, as a proof of this, a trial which he had caused to be made on the Puy-de-Dôme, where a balloon partly filled with air at the base, on being carried to the summit, was entirely distended ; it shrunk again as the party descended the mountains, and regained its former volume at the foot. He made some observations, also, on the changes to which the column of mercury is exposed, while kept at the same place, proceeding from the variations of the weather. He did not, indeed, divine all the barometrical uses of this instrument, though he seems to have accomplished more in this way than any one of his contemporaries.

If we except the mathematical inquiry respecting the cycloid, which was taken up rather as a diversion during his last illness, it may be said, that Pascal's scientific labors terminated when he had attained the age of thirty. It is not surprising, then, that their results should hardly appear so numerous and brilliant as those obtained by one or two of his illustrious contemporaries in an age which was the most remarkable, perhaps, for the progress of science and the development of the human mind, of any in the VOL. LX. - NO. 127.

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history of the world. But as indications of what he night have done in a longer period, or under more favorable circumstances, -as evidence of the vast power and fertility of his youthful intellect, they will never cease to command the wonder and admiration of mankind. If his life had been protracted to the ordinary limit, if suffering and disease bad not perpetually discouraged him, if his ambition bad been greater, or if it had not been so early checked and turned into a different channel, we can hardly doubt that he would have stood among the foremost of the great promoters of science in modern times.

The father of Pascal died in 1651; and two years afterwards, his sister Jacqueline, to whom he was tenderly attached, retired for ever from the world, by uniting herself to the company of pious recluses at Port Royal. Anxious to show the fervor of her religious faith, and her grateful feelings towards the brother who had first directed her own steps to the path of peace, she sought to win him also from the world, by causing him to renounce his former studies, and to seek only for the things of heaven. Various circumstances aided the execution of this pious scheme. An attack of paralysis, several years before, had nearly deprived him of the use of his legs, and diseases of the nervous system and the stomach had now brought him to the verge of the grave. There was no course left for him but to abandon his engrossing labors, at least for a season, to turn bis thoughts to other subjects, and patiently to await either the partial restoration of his health, or a final release from earthly suffering. During the tedious hours of illness, his mind reverted to the religious counsels he had received in his youth. His father had carefully sown in his mind the seeds of piety and Christian faith. These had remained quiet, though not wholly inoperative, during his early manhood, while the whole force of his intellect was directed to scientific pursuits. But they sprang up with a most luxuriant growth, when these pursuits were forcibly interrupted for a time by physical suffering. The objects for which he had hitherto labored so strenuously now lost all value in his eyes. The memory of youthful triumphs was no longer pleasant ; the reputation he had already gained, the hopes of still greater distinction which he had once cherished, were now ranked among the vain joys and aspirations of a world which seemed to be

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