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weight. Were it not for this property, evaporation could not be produced; and, consequently, no clouds, rain, nor dew, could be formed, to water and fertilize the different regions of the earth. But, in consequence of this wonderful property, the ocean becomes an inexhaustible cistern to our world. From its expansive surface are exhaled those vapours which supply the rivers, and nourish the vegetable productions of every land. "The air and the sun," says an elegant writer, "constitute the mighty engine which works without intermission to raise the liquid treasures; while the clouds serve as so many aqueducts to convey them along the atmosphere, and distribute them, at seasonable periods, and in regular proportions, through all the regions of the globe."

Notwithstanding the properties now stated, motion was still requisite, to ensure all the advantages we now derive from the liquid element. Had the whole mass of waters been in a stagnant state, a thousand inconveniences and disastrous consequences would have inevitably ensued. But the All-Wise Creator has impressed upon its various masses a circulating motion, which preserves its purity, and widely extends its beneficial influence. The rills pour their liquid stores into the rivers; the rivers roll their watery treasures into the ocean; the waters of the ocean, by a libratory motion, roll backwards and forwards every twelve hours, and, by means of currents, and the force of winds, are kept in constant agitation. By the solar heat, a portion of these waters is carried up into the atmosphere, and, in the form of clouds, is conveyed by the winds over various regions; till, at last, it descends in rain and dew, to supply the springs " which run among the hills." So that there is a constant motion and circulation of the watery element, that it may serve as an agent for carrying forward the various processes of nature, and for ministering to the wants of man and beast.

In fine, were the waters in a state of perpetual stagnation, the filth of populous cities would be accumulated to a most unwholesome degree, the air would be filled with putrid exhalations, and the vegetable tribes would languish and die. Were they deprived of the property of being

evaporated (in which state they occupy a space 1400 times greater than in their liquid state,) rain and dew could never be produced, and the earth would be turned into "a dry and parched wilderness;" neither grass nor corn could be sufficiently dried to lay up for use; our clothes, when washed, could never be dried; and a variety of common operations, which now conduce to our convenience and comfort, could never be carried on. But the infinite wisdom of the Creator, foreseeing all the effects which can possibly arise from these principles of nature, has effectually provided against such disasters, by arranging all things, in number, weight, and measure, to subserve the beneficial ends for which they were ordained. "He causeth the vapours to ascend from the ends of the earth; he sendeth the springs into the valleys, which run among the hills. They give drink to every beast of the field; the wild asses quench their thirst. By them the fowls of heaven are refreshed, which sing among the branches. He watereth the hills from his chambers, and the earth is satisfied with the fruit of his works."

Let us now attend to the atmosphere, in the constitution of which the wisdom of God is no less conspicuous than in the other departments of nature.

The atmosphere is one of the most essential appendages to the globe we inhabit, and exhibits a most striking scene of Divine skill and omnipotence. The term atmosphere is applied to the whole mass of fluids, consisting of air, vapours, electric fluid, and other matters, which surrounds the earth to a certain height. This mass of fluid matter gravitates to the earth, revolves with it in its diurnal rotation, and is carried along with it in its course round the sun every year. It has been computed to extend about 45 miles above the earth's surface, and it presses on the earth with a force proportioned to its height and density. From experiments made by the barometer, it has been ascertained, that it presses with a weight of about 15 pounds on every square inch of the earth's surface; and, therefore its pressure on the body of a middle-sized man, is equal to about 32,000 lbs. or 14 tons avoirdupois, a pressure which would be insupportable, and even fatal,

were it not equal in every part, and counterbalanced by the spring of the air within us. The pressure of the whole atmosphere upon the earth, is computed to be equivalent to that of a globe of lead 60 miles in diameter, or about 5,000,000,000,000,000 tons; that is, the whole mass of air which surrounds the globe, compresses the earth with a force or power equal to that of five thousand millions of millions of tons.* This amazing pressure is, however, essentially necessary for the preservation of the present constitution of our globe, and of the animated beings which dwell on its surface. It prevents the heat of the sun from converting water, and all other fluids on the face of the earth, into vapour; and preserves the vessels of all organized beings in due tone and vigour. Were the atmospherical pressure entirely removed, the elastic fluids contained in the finer vessels of men and other animals, would inevitably burst them, and life would become extinct;† and most of the substances on the face of the earth, particularly liquids, would be dissipated into vapour.

The atmosphere is now ascertained to be a compound substance, formed of two very different ingredients, termed oxygen and nitrogen gas. Of 100 measures of atmospheric air, 21 are oxygen, and 79 nitrogen. The one,

*See Appendix, No. II.

†The necessity of the atmospherical pressure, for the comfort and preservation of animal life, might be illustrated by the effects experienced by those who have ascended to the summits of very high mountains, or who have been carried to a great height above the surface of the earth in balloons. Acosta, in his relation of a journey among the mountains of Peru, states, that "he and his companions were suprised with such extreme pangs of straining and vomiting, not without casting up of blood too, and with so violent a distemper, that they would undoubtedly have died had they remained two or three hours longer in that elevated situation." Count Zambeccari, and his companions, who ascended in a balloon, on the 7th November, 1783, to a great height, found their hands and feet so swelled, that it was necessary for a surgeon to make incisions in the skin. In both the cases now stated, the persons ascended to so great a height, that the pressure of the atmosphere was not sufficient to counter balance the pressure of the fluids of the body,

namely, oxygen, is the principle of combustion, and the vehicle of heat, and is absolutely necessary for the support of animal life, and is the most powerful and energetic agent in nature. The other, is altogether incapable of supporting either flame or animal life. Were we to breathe oxygen air, without any mixture or alloy, our animal spirits would be raised, and the fluids in our bodies would circulate with greater rapidity; but we should soon infallibly perish by the rapid and unnatural accumulation of heat in the animal frame. If the nitrogen were extracted from the air, and the whole atmosphere contained nothing but oxygen, or vital air, combustion would not proceed in that gradual manner which it now does, but with the most dreadful and irresistible rapidity. Not only wood and coals, and other substances now used for fuel, but even stones, iron, and other metallic substances, would blaze with a rapidity which would carry destruction through the whole expanse of nature. If even the proportions of the two airs were materially altered, a variety of pernicious effects would instantly be produced. If the oxygen were less in quantity than it now is, fire would lose its strength, candles would not diffuse a sufficient light, and animals would perform their vital functions with the utmost difficulty and pain. On the other hand, were the nitrogen diminished, and the oxygen increased, the air taken in by respiration would be more stimulant, and the circulation of the animal fluids would become accelerated; but the tone of the vessels thus stimulated to increased action, would be destroyed, by too great an excitement, and the body would inevitably waste and decay. Again, were the oxygen completely extracted from the atmosphere, and nothing but nitrogen remained, fire and flame would be extinguished, and instant destruction would be carried throughout all the departments of vegetable and animated nature. For a lighted taper will not burn for a single moment in nitrogen gas, and if an animal be plunged into it, it is instantly suffocated.

Again, not only the extraction of any one of the component parts of the atmosphere, or the alteration of their respective proportions, but even the slightest increase or

diminution of their specific gravity, would be attended with the most disastrous effects. The nitrogen is found to be a little lighter than common air, which enables it to rise towards the higher regions of the atmosphere. In breathing, the air which is evolved from the lungs, at every expiration, consists chiefly of nitrogen, which is entirely unfit to be breathed again, and therefore rises above our heads before the next inspiration. Now, had nitrogen, instead of being a little lighter, been a slight degree heavier than common air, or of the same specific gravity, it would have accumulated on the surface of the earth, and particularly in our apartments, to such a degree as to have produced diseases, pestilence, and death, in rapid succession. But being a little lighter than the surrounding air, it flies upwards, and we never breathe it again, till it enter into new and salutary combinations. Such is the benevolent skill which the Author of Nature has displayed, for promoting the comfort and preservation " of every thing that lives."*

Farther, were the air coloured, or were its particles much larger than they are, we could never obtain a distinct view of any other object. The exhalations which rise from the earth being rendered visible, would disfigure the rich landscape of the universe, and render life disagreeable. But the Almighty, by rendering the air invisi

The necessity of atmospherical air for the support of life, was strikingly exemplified in the fate of the unhappy men who died in the Black-hole of Calcutta. On the 20th of June, 1756, about 8 o'clock in the evening, 146 men were forced, at the point of the bayonet, into a dungeon only 18 feet square. They had been but a few minutes confined in this infernal prison, before every one fell into a perspiration so profuse, that no idea can be formed of it. This brought on a raging thirst, the most difficult respiration, and an outrageous delirium. Such was the horror of their situation, that every insult that could be devised against the guard without, and all the opprobrious names that the Viceroy and his officers could be loaded with, were repeated, to provoke the guard to fire upon them and terminate their sufferings. Before 11 o'clock the same evening, onethird of the men were dead; and, before 6 next morning, only 23 came out alive, but most of them in a high putrid fever. All these dreadful effects were occasioned by the want of atmospheric air, and by their breathing a superabundant quantity of the nitrogen emitted from their lungs.

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