purpose than water, and therefore used, in place of it, mercury, which is about fourteen times as heavy. Having closed a glass tube hermetically at one end, he filled it with mercury, and then brought the open end inverted into a vessel partly filled with the same substance, taking care that the end of the tube should be under the surface of the mercury in the open vessel. He thus observed that the column in the tube contracted till. the top of it stood at between twenty-nine and thirty inches above the mercury in which it was immersed. Having marked the specific gravity of the mercury, the weight of the column of air between the mercury and the top of the tube became of course apparent, from the respective proportions of the columns of air and mercury and the whole length of the tube. It should be stated, that in 1631, that is, twelve years before Torricelli's observations, Descartes, the French philosopher, had made the same observation, although he does not appear to have turned it to any account.

This was the first and the great step; but whether Torricelli is entitled to the honour of having been the first to discover the true reason of the depression of the mercury, is uncertain ; at any rate, there was at once an end of the "vacuum" assertions, and a great step was gained towards sound philosophical principles, and to that merit he is most decidedly entitled.

The subject had excited too much attention to be dropped; and Pascal Mersenne in France, and Boyle in England, took it up. Of these, Pascal appears to have been the most sensible and rational observer. He very reasonably argued, that if it were the column of air which occasioned the alteration of the column of mercury, the higher the point in the atmosphere, the higher the mercury would stand in the tube; and Boyle had well prepared the way for him by testing the barometer with airs of different densities, by means of the air-pump.

To carry this principle to some practical conclusion, Pascal requested his friend, M. Perrier, to ascertain the height at

which the mercury stood at the base and on the summit of the Ruy de Dome, one of the loftiest mountains in the province of Auvergne. The result perfectly answered his expectations. At the base, the mercury stood at a height of 26 inches, while on the summit it was only 23 inches; the mountain being between three and four thousand feet above the level of the sea. A like result was afterwards ascertained by Pascal himself; and he also discovered that the same rule prevailed and was very sensibly shown, in the ascent of a private house and a church tower.

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Thus the fact was satisfactorily established, that the weight of a column of air was equal to that of a column of mercury about twenty-eight inches high, that is, a pressure of about fifteen pounds on a square inch.

The barometer only required the addition of an index and a weather-glass, to give a fair and true announcement of the state and weight of the atmosphere. The instruments are now manufactured in several different forms, but the principle is the same in all, and repeated observations during the ascent of the loftiest mountains in Europe and America, have confirmed the truth of barometrical announcements; for by its indications, the respective heights of the acclivities in high regions can now be ascertained by means of this instrument better than by any other course, with this advantage, too, that no proportionate height need be known to ascertain the altitude.

In navigation the barometer has become an important element of guidance, and a most interesting incident is recounted by Capt. Basil Hall, indicative of its value in the open sea. While cruising off the coast of South America, in the Medusa frigate, one day, when within the tropics, the commander of a brig in company was

dining with him. After dinner, the conversation turned on the natural phenomena of the region, when Captain Hall's attention was accidentally directed to the barometer in the state-room where they were seated, and to his surprise he observed it to evince violent and frequent alteration. His experience told him to expect bad weather, and he mentioned it to his friend. His companion, however, only laughed, for the day was splendid in the extreme, the sun was shining with its utmost brilliance, and not a cloud specked the deep blue sky above. But Captain Hall was too uneasy to be satisfied with bare appearances. He hurried his friend to his ship, and gave immediate directions for shortening the top hamper of the frigate as speedily as possible. His lieutenants and the men looked at him in mute surprise, and one or two of the former ventured to suggest the inutility of the proceeding. The captain, however, persevered. The sails were furled; the topmasts were struck; in short, everything that could oppose the wind was made as snug as possible. His friend, on the contrary, stood in under every sail.

The wisdom of Captain Hall's proceedings was, however, speedily evident; just, indeed, as he was beginning to doubt the accuracy of his instrument. For hardly had the necessary preparations been made, and while his eye was ranging over the vessel to see if his instructions had been obeyed, a dark hazy hue was seen to rise in the horizon, a leaden tint rapidly overspread the sullen waves, and one of the most tremendous hurricanes burst upon the vessels, that ever seaman encountered on his ocean home. The sails of the brig were immediately torn to ribbons, her masts went by the board, and she was left a complete wreck on the tempestuous surf which raged around her, while the frigate was driven wildly along at a furious rate, and had to scud under bare poles across the wide Pacific, full three thousand miles, before it could be said that she was in safety from the blast.

THE TELESCOPE.

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HAT wonders yet remain to be discovered by the Telescope we know not, although every year brings to light some new world by its aid, that had stood unobserved, in the immensity of space, by the eye of man, since the day it was first rolled into the illimitable and starry expanse, at the bidding of the Omnipotent. Through the power of this wonderful instrument the human eye is enabled to sweep through vast systems-a boundless extent of space that, had the swiftest race-horse which ever struck its hoof upon the earth, set out from the orb of Uranus, about three thousand years ago, and plunged on in his headlong course day and night without ceasing, he would not yet have traversed the half of this huge diameter that extends 3,600,000,000 of miles. Even by the sides of our system, where but few stars are visible, the gigantic telescope of the Earl Rosse has been turned, and there firmaments have been discovered like our own, covered with countless stars, seeming in that vast distance like a spot glittering with the dust of thousands of diamonds, one almost appearing to touch another, yet each lying from each millions of miles apart, and every one a huge world to which our own earth bears no more proportion than a single daisy does to the field in which it grows. By the aid of the telescope we have been enabled to

distinguish objects in the moon; to see huge volcanoes sending forth their awful fires; to distinguish mountains ranged pile above pile with vast yawning pits at their feet, some of which appear to be 22,000 feet deep. By it we are enabled to trace the course of the fiery comet, as it goes threading its terrible way between the vast worlds that circle round us, until it is lost in that immense sea of space which, like eternity, seems to have no shore.

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The telescope can scarcely be called a discovery; its construction may, but it was by accident that a poor Dutch spectacle-maker first threw two lenses together in an influential position, and by chance stumbled upon the origin of the most wonderful instrument that was ever perfected by man. magnitude of the heavenly bodies," says a writer in the "North British Review," "and their almost infinite distance from us, and from each other, fill the mind with views at once magnificent and sublime, while our ideas of the Creator's power rise with the number and magnitude of his works, and expand with the ever-widening bounds which they occupy. The telescope was a mighty gift which God gave to man, to place before him and beside him new worlds, and systems of worlds, probably the abodes of spirits-the dwellings of saints that have suffered, and of sages that have been truly wise.

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When viewed from the highest peak of a mountainous region, our own globe is the largest magnitude we can perceive, and the circuit of its visible horizon the greatest distance we can scan; but vast as are these units in relation to the eyeball by which they are seen, they are small when compared with the globe itself, or with its circular outline. The navigator who has measured the earth's circuit by his hourly progress, or the astronomer who has paced a degree of the meridian, can alone form a clear idea of velocity when he knows that light moves through a space equal to the circumference of the earth in the eighth part of a second of time-in the twinkling of an eye.