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been suspected. The observation of the instrument being carried still farther, it was found, that in serene dry weather the mercury generally stood high, and that before and during storms and rain it fell :the instrument therefore might serve as a prophet of the weather, becoming a precious monitor to the husbandman or the sailor.
The reasons why the barometer falls before wind and rain will be better understood a few pages hence; but we may remark here, that when water which has been suspended in the atmosphere, and has formed a part of it, separates as rain, the weight and bulk of the mass are diminished: and that wind must occur when a sudden condensation of aeriform matter, in any situation, disturbs the equilibrium of the air, for the air around will rush towards the situation of diminished pressure.
To the husbandman the barometer is of considerable use, by aiding and correcting the prognostics of the weather which he draws from local signs familiar to him; but its great use as a weather-glass seems to be to the mariner, who roams over the whole ocean, and is often under skies and climates altogether new to him. The watchful captain of the present day, trusting to this extraordinary monitor, is frequently enabled to take in sail and to make ready for the storm, where, in former times, the dreadful visitation would have fallen upon him unprepared.—The marine barometer has not yet been in general use for many years, and the author was one of a numerous crew who probably owed their preservation to its almost miraculous warning. It was in a southern latitude. The sun had just set with placid appearance, closing a beautiful afternoon, and the usual mirth of the evening watch was proceeding, when the captain's order came to prepare with all haste for a storm. The barometer had begun to fall with appalling rapidity. As yet, the oldest sailors had not perceived even a threatening in the sky, and were surprised at the extent and hurry of the preparations; but the required measures were not completed, when a more awful hurricane burst upon them than the most experienced had ever braved. Nothing could withstand it; the sails already furled and closely bound to the yards, were riven away in tatters: even the bare yards and masts were in great part disabled; and at one time the whole rigging had nearly fallen by the board. Such, for a few hours, was the mingled roar of the hurricane above, of the waves around, and of the incessant peals of thunder, that no hu
man voice could be heard, and amidst the general consternation, even the trumpet sounded in vain. In that awful night, but for the little tube of mercury which had given warning, neither the strength of the noble ship, nor the skill and energies of the commander, could have saved one man to tell the tale. On the following morning the wind was again at rest, but the ship lay upon the yet heaving waves, an unsightly wreck.
The marine barometer differs from that used on shore, in having its tube contracted in one place to a very narrow bore, so as to prevent that sudden rising and falling of the mercury, which every motion of the ship would else occasion.
Civilized Europe is now familiar with the barometer and its uses, and therefore, that Europeans may conceive the first feelings connected with it, they almost require to witness the astonishment or incredulity with which people of other parts still regard it. A Chinese once conversing on the subject with the author, could only imagine of the barometer, that it was a gift of miraculous nature, which the God of Christians gave them in pity, to direct them in the long and perilous voyages which they undertook to unknown seas.
A barometer is of great use to persons employed about those mines in which hydrogen gas, or fire-damp, is generated and exists in the crevices. When the atmosphere becomes unusually light, the hydrogen being relieved from a part of the pressure which ordinarily confines it to its holes and lurking places, expands or issues forth to where it may meet the lamp of the miner, and explode to his destruction. In heavy states of the atmosphere, on the contrary, it is pressed back to its hiding places, and the miner advances with safety.
We see from this that any reservoir or vessel containing air would itself answer as a barometer if the only opening to it were through a long tubular neck, containing a close sliding plug, for then according to the weight and pressure of the external air the density of that in the cavity would vary, and all changes would be marked by the position of the moveable plug. A beautiful barometer has really been made on this principle by using a vessel of glass, with a long slender neck, in which a globule of mercury is the moveable plug.
The state of the atmosphere, as to weight, differs so much at different times in the same situation, as to produce a range of about three inches in the height of the mercurial barometer, that is to say, from
twenty-eight to thirty-one inches. On the occasion of the great Lisbon earthquake, however, the mercury fell so far in the barometers, even in Britain, as to disappear from that portion at the top usually left uncovered for observation. The uncovered part of a barometer is commonly of five or six inches in length, with a divided scale attached to it, on which the figures 28, 29, &c., indicate the number of inches from the surface of the mercury at the bottom to the respective divisions:-on the lower part of the scale the words wind and rain are generally written, meaning that when the mercury sinks to them, wind and rain are to be expected; and on the upper part, dry and fine appear, for a corresponding reason; but we have to recollect, that it is not the absolute height of the mercury which indicates the existing or coming weather, but the recent change in its height:-a falling barometer usually telling of wind and rain; a rising one of serene and dry weather.
The barometer answers another important purpose, besides that of a weather-glass—in enabling us to ascertain readily the height of mountains, or of any situation to which it can be carried.
As the mercurial column in the barometer is always an exact indication of the tension or pressure produced in the air around it by the weight of air above its level, being indeed, as explained in the foregoing paragraphs, of the same weight as a column of the air of equal base with itself, and reaching from it to the top of the atmosphere— the mercury must fall when the instrument is carried from any lower to any higher situation, and the degree of falling must always tell exactly how much air has been left below. For instance, if thirty inches barometrical height mark the whole atmospheric pressure at the surface of the ocean, and if the instrument be found, when carried to some other situation, to stand at only twenty inches, it proves that one-third of the atmosphere exists below the level of the new situation. If our atmospheric ocean were of as uniform density all the way up as our watery oceans, a certain weight of air thus left behind in ascending would mark everywhere a change of level nearly equal, and the ascertaining any height by the barometer would become one of the most simple of calculations:-the air at the surface of the earth being about twelve thousand times lighter than its bulk of mercury, an inch rise or fall of the barometer would mark everywhere a rise or fall in the atmosphere of twelve thousand inches or one thousand feet. But
owing to the elasticity of air, which causes it to increase in volume as it escapes from pressure, the atmosphere is rarer in proportion as we ascend, so that to leave a given weight of it behind, the ascent must be greater, the higher the situation where the experiment is made; the rule therefore of one inch of mercury for a thousand feet, holds only for rough estimates near the surface of the earth. The precise calculation, however, for any case, is still very easy; and a good barometer, with a thermometer attached, and with tables, or an algebraical formula expressing all the influencing circumstances, enables us to ascertain elevations much more easily, and in many cases more correctly, than by trigonometrical survey.
The weight of the whole atmospherical ocean surrounding the earth being equal to that of a watery ocean of thirty-four feet deep, or of a covering of mercury of thirty inches, and the air found at the surface of the earth being eight hundred and forty times lighter than water, if the same density existed all the way up, the atmosphere would be 34 times 840, or about 28,000 feet high, which is equal to five miles and a half. On account of the greater rarity, however, in the superior regions, it really extends to a height of nearly fifty miles. From the known laws of aerial elasticity, we can deduce what is found to hold in fact, that one half of all the air constituting our atmosphere exists within three miles and a half from the earth's surface; that is to say, under the level of the summit of Mount Blanc. A person, unaccustomed to calculation, would suppose the air to be more equally distributed through the fifty miles than this rule indicates, as he might at first also suppose a tube of two feet diameter to hold only twice as much as a tube of one foot, although in reality it holds four times as much.
In carrying a barometer from the level of the Thames to the top of St. Paul's Church in London, or of Hampstead Hill, the mercury falls about half an inch, marking an ascent of about five hundred feet. On Mount Blanc it falls to half of the entire barometric height, marking an elevation of fifteen thousand feet; and in Du Luc's famous balloon ascent it fell to below twelve inches, indicating an elevation of twentyone thousand feet, the greatest to which man has ever ascended from the surface of his earthly habitation.
The extreme rarity of the air on high mountains must of course affect animals. A person breathing on the summit of Mount Blanc,
although expanding his chest as much as usual, really takes in at each inspiration only half as much air as he does below-exhibiting a contrast to a man in the diving-bell, who at thirty-four feet under water is breathing air of double density, at sixty-eight feet of triple, and so on. It is known that travellers, and even their practised guides, often fall down suddenly as if struck by lightning, when approaching lofty summits, on account chiefly of the thinness of the air which they are breathing, and some minutes elapse before they recover. In the elevated plains of South America, the inhabitants have larger chests than the inhabitants of lower regions-another admirable instance of the animal frame adapting itself to the circumstances in which it is placed. It appears from all this, that although our atmosphere be fifty miles high, it is so thin beyond three miles and a half, that mountain ridges of greater elevation are nearly as effectual barriers between nations of men, as islands or rocky ridges in the sea are between the finny tribes inhabiting the opposite coasts.
21.-A COMPLAINT OF THE DECAY OF BEGGARS IN THE METROPOLIS.
[CHARLES LAMB-what shall we say of the most original, most quaint, most simple, most touching, of all modern essayists? No critical line and level can measure the sinuosities of his rich and overflowing runlet of thought; no plummet can gauge the depth of his quiet but most genial humour. Few are his writings;-but there are, in their way, not many higher things in any language. They are finished works of art. How did he form his style? It is the revelation of his own nature. It lets us into the innermost depths of the man as completely as Montaigne shows us himself in all his nakedness; but there are no painful exposures of gross desires and unlawful imaginings. He has as keen a sense of the hiding-places of vice and meanness as Swift; but he has no truculent abuse or withering sarcasm for what he dislikes. He has a large toleration of all human infirmity, and a cordial love of all human excellence. He deposits no offerings on the altars of conventional opinions; he mouths no common-places about goodness and greatness; he blindly worships neither purple nor rags. He delights in queer books and queer men and women. He sees in what is called a character some rich fruit under a rough rind; and he gets at the juice through the husk in a way which is, to say the least,