beholden for the twilight, or that surprising phenomenon of nature by which we enjoy the real presence of the sun when he is actually below the horizon* ! Were it not for the reflective quality of the air, by which indeed the light is parted, we would behold the sun in his splendour, and observe a brightness in that part of the heavens in which he happened to be, but on turning round how cheerless would be the prospect; there, darkness visible would reign in the heavens, although the stars and planets would glimmer at noon day‡; and were it not for the refractive property of this fluid, by which the oblique rays of the great luminary are broken off from a straight course, and turned towards the earth, the transition from the horrors of night to the light of day must have been instantaneous, and instead of those beneficial harbingers, by which the outgoings of the morning and evening are made to rejoice, and the long and dismal nights of the polar regions stript of their horrors, the optic nerves would have been overpowered by the sun rising in all his glory, and the moment he sunk beneath the horizon, the bewildered traveller left to grope in the dark.

Although the air cannot be frozen or perceived by the eye, for the wise reasons already noticed, yet it is capable of being condensed and rarified to an astonishing degree||;

and

*For the better understanding of this, let any person put a shilling into a basin, and then retire until he can just observe its outer edge visible over the inner edge of the vessel; in that position let some person fill up the basin with water, the WHOLE shilling, by being seen through a denser medium, will instantly become visible to the person who could only before observe its outer edge.

+ One of the questions the Lord put to Jos out of the whirl wind,-was, By what way is the light parted." Job, xxxviii. 24.

M. de SAUSSURE, when on the top of Mount Blanc, which is elevated 5101 yards above the level of the sea, and where consequently the atmosphere must be more rare than ours, says, that the moon shone with the brightest splendour in the midst of a sky black as ebony; while Jupiter, rayed like the sun, rose from behind the mountains in the east.

The twilight is said to be of longer duration at the Poles than any where else; there the sun, reflecting his rays obliquely, and not sinking much below the horizon of the neighbouring people, their nights though long, are almost all along attended with twilight!

So much so, that the air in a house may be compressed as to be made to enter a cavity not larger than the eye of a needle, and the

and by these remarkable properties, together with its weight and elasticity, it is admirably fitted for some of its most essential uses, and, perhaps, none more so than for the business of animal respiration*.

Perhaps some of my readers may be surprised at the bare mention of the weight of a substance, which has been proverbially compared to a trifle for its lightness, and they may wonder still more when I speak of its elasticity, when they have been taught to consider it an unresisting medium; but what will such think when I boldly assert, that we are literally plunged into a sea of air, and of such gravity and pressure, as to be equal, on the body of a man of moderate size, to the weight of 20,000 lbs.†! "Tremendous consideration," says the reflective HERVEY, "should the ceiling of a room, or the roof of a house, fall upon us with half that force, what destructive effects must ensue! Such a force would infallibly drive the breath from our lungs, or break every bone in our bodies, yet so admirably has the divine wisdom contrived this ærial fluid, and so nicely counterpoised its dreadful power, that we receive not the slightest hurt; we suffer no manner of inconvenience, we even enjoy the load. Instead of being as a mountain on our loins, it is like wings to our feet, or like sinews to our limbs. Is not this common ordination of providence thus considered, something like the miracle of the burning bush; whose tender and combustible substance, though in the midst of flames, was neither consumed nor injured.”

But how are we to account for this miraculous preservation? It is owing to the elasticity or spring of the internal

air

contents of a nut-shell so expanded, as to fill a sphere of unknown dimensions! If an empty bladder, with its neck tied close, is laid before the fire, the heat will so rarify the small quantity of inclosed air, as to make it extend the bladder to its full dimensions, and if not then timeously removed, will at last break it with the report of a gun. Sir ISAAC NEWTON thinks the air capable of diffusing itself into above a million of times more space than it before possessed!

* In this act, so necessary for the prolongation of life, the air, by. its weight and condensing power, is forced and compressed into the lungs, while, by its elastic and expanding property, it is thrown out again in the act of breathing.

† According to GOLDSMITH, the computation has been found to nearly double that amount, which makes the wonder still greater!

air within all bodies, which although small in proportion, is wisely made to balance, resist, and equiponderate that which is without, notwithstanding the height of its column*,

Although, in casting our eyes upwards, we do not observe any boundery to the vast expanse, we are not to consider that the atmosphere is unlimited. On the contrary, we are taught by the most rational calculations, that if it extends much beyond 45 or 50 miles, it becomes so exceeding ly rare, as to be unfit for the purposes for which the lower regions are so well adaptedt. It is seldom indeed sufficient ly dense at the height of two miles to be able to bear up the clouds, so that to whatever perfection our modern aeronauts may bring the art of Balloon-navigation, there is not the smallest probability of their being able to escape from the earth to another planet. The atmosphere has its limits as well as the ocean, and not ouly are those massy bodies that are made to move in the lower parts of this great outwork of our globe, confined by laws, firm as chains of adamant, but the thinnest vapour, the minutest atom, the most subtile effluvia that ascend the higher regions, and gain as it were the outskirts of creation, are checked in their career by the powerful mandate of the GOD OF NATURE, and forced to return and execute his orders.

Happy indeed for the world is this ordination, for, if the philosophical axiom be true, that things must continue as at the beginning with respect to the quantity of matter contained in the universe, and that, if it were possible that a single

atom

*The elasticity and resistance of the air cannot be demonstrated by a more simple experiment, than by pressing with the hand on a bladder in which it is confined,-and the weight and pressure of the atmosphere may be explained whout the aid of the air-pump or other philosophical instrument, merely by taking a common saucer, filled with water, and turning down a teacup into it, with a piece of flaming paper inside. As the fire destroys the internal air in the cup, a sort of vacuum will take place, an the pressure of the outward air on the water in the saucer will make it disappear and fill it up.

The atmosphere. at the height of 50 miles, is said to be so rare, that it has no sensible effect on the rays of light. At the height of 45 miles it loses the power of refraction; at 41 miles it is supposed to be rarified to that degree, as to occupy 3000 times the space it does here; and Dr. GREGORY observes, that it is generally agreed that there are no clouds at the height of 4 or 5 miles.

atom could be lost, the harmony of creation would be destroyed, what direful consequences must ensue were the daring spirits of adventurous men not confined by unalterable laws, and the imperceptible atoms which float in the atmosphere not laid under restraint, by that command, which says to the troubled waves of the ocean, "Hitherto shalt thou come, and no farther."

THE USES OF THE ATMOSPHERE.

I have already mentioned several of the uses of this invaluable and all-pervading fluid, in my humble attempt to point out some of its most remarkable peculiarities, and all I can now do is, to notice a few, and but a very few more, of the many unspeakable blessings and advantages derived from this necessary appendage, which the BOUNTI FUL BENEFACTOR OF THE HUMAN RACE has attached to our globe

The air, in a peculiar manner, may be said, to constitute the very essence of which life is made. When the Lord created man of the dust of the ground, He breathed into him the breath of life, when man became a living soul; and the experience of all ages abundantly testifies, that when men cease to breathe, which is performed by means of the air, they cease to exist. Many days, it has been observed we might live, or even whole months, without the light of the sun or the glimmering of a star, whereas, if we are deprived only for a few minutes of this ærial support, we sicken, we faint, we die. How thankful than ought we to be, that of this indispensible neccssary of life, no person can deprive us. The treasures of the earth, the verdure of the fields, and even the refreshments of the stream, often contribute to the luxuries of the great, while the less fortunate can only behold them as humble spectators; but, in the words of an eminent naturalist, "the air no limitations can bound, nor any landmarks restrain. In this benign element, all mankind can boast an equal possession; and for this we all have equal obligations to Heaven."

It is equally beneficial to all the branches of the animal creation; for although some creatures dwell in the very bowels of the earth, or swim in the unmeasurable depths of sea, yet it has been demonstrated by experiment, that no

the

sooner

sooner are they totally deprived of air than they cease to live. By the same air, also, that preserves animal life, flame is fed and cherished.-We all know the utility of fire, and the many inconveniences to which we would be exposed were we deprived of that necessary element, but without air, in vain would the faggots be piled in a heap, in vain would we apply the lighted torch. Every attempt to set the hearth in a blaze, in order to render our habita tions more comfortable during the chilling damps of win ter, and every effort to dispel the midnight gloom by the cheering candle, would prove abortive. Take but away the surrounding air, life expires, and the lighted taper goes out in darkness*.-Plants are also dependent on the air for support and nourishment, and they cannot possibly exist without it. They are continually imbibing fresh nutri ment from the atmosphere. It is this wondrous fluid that helps to transfuse vegetable vigour into the trunk of the mighty oak, and gives a blooming gaiety to the spreading

rose.

And how wisely is its consistence calculated for answering these important purposes. It is neither too thick nor too thin; too gross or too attenuated. It rushes with ease into our lungs in order to inflate them in the act of respira tion; it forces its way into the most minute tubes of the vegetable tribes. In fact, as Mr DERHAM observes, it is a subtile and penetrating matter, "fit to pervade other bodies, to penetrate into the inmost recesses of nature; to excite, animate, and spiritualize; and, in short, to be the very soul of this lower world.”

But what is very remarkable, this wonderful fluid, so necessary for the existence of bodies, is also made use of as a most powerful agent in the hand of providence for their destructiont. It is a chaos containing all kinds of menstrua, and consequently possessing powers for dissolv.

ing

* An ordinary candle is said to consume about a gallon of air in a minute !

Metallic substances are valuable for their durability in resisting the effects of humidity and of air but BOERHAAVE asserts, that he had seen pillars of iron so reduced by air, that they might be crumbled to dust between the fingers.