where find corroborating testimony to the same great truths! So the mathematician, though he has demonstrated a proposition by strict definition of terms, and sure process of ratiocination, is still pleased to discover other and independent methods of demonstrating the. same truth.

I invite your attention more particularly this afternoon, young gentlemen, while I attempt to illustrate the wisdom and benevolence of Deity, as exhibited in the constitution of atmospheric air.

The atmosphere, as is well known, is an extremely elastic fluid, generally considered invisible, entirely surrounding the earth, and extending above its surface to the height of about forty-five miles. It is a material substance, and composed of particles so exceedingly minute, that they penetrate the smallest cavities in all bodies. Its weight* or pressure upon the surface of the earth is about fifteen pounds to every square inch, and is equal to that of a sea of mercury extending over the whole earth, (supposing it free from all inequalities of surface,) about thirty inches deep, or a sea of water thirty-three feet deep. The volume any particular quantity occupies is found to depend upon the temperature and pressure to which it is subjected, the lower strata being much more dense than the upper, in consequence of the pressure of the superincumbent portions. Usually, near the level of the sea, at the temperature of 60° Fah., one hundred cubic inches weigh a little more than thirty-one grains, Troy.

This fluid is absolutely essential to the existence of both animal and vegetable life. There can indeed be no question but that it was within the compass of omnipotent power to create both animals and vegetables with powers that would enable them to live in a perfect vacuum, or in atmospheres entirely different from the existing one; but the divine wisdom and benevolence are manifested in nature as well as in morals, in the beautiful harmony of all the parts, in the adaptation of all the parts to each other, and each to the whole. A part, therefore, of the handiwork of the Creator requiring for its con tinued existence and perfect development such a substance as atmos. pheric air to be constantly present, we find it supplied in such a manner that it comes without being sought, and produces its prope effect without thought or design on the part of any created intelligence.

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But my design leads me to point out, a little more in detail, the beautiful adaptation of atmospheric air to serve the purposes for which it is designed, thus evincing the wisdom and goodness of the Creator.

1. To render atmospheric air capable of serving the purposes designed by the Creator, it is absolutely necessary it should possess the gaseous form. All matter exists in the solid, liquid, or gaseous form, and, unquestionably, the matter of the atmosphere might have been created a solid or a liquid, as well as a gas, but the latter state only would enable it to subserve the wants of other parts of the creation, and this is the form or state in which we find it. Next after the ga eous, the liquid form would seem to be most desirable, but how much less adapted would it then be to serve the purposes of man and the other parts of creation!

*The weight of the whole atmosphere surrounding the earth is computed to be about equal to that of a globe of lead sixty miles in diameter.

2. The amount of atmospheric pressure appears to be such as best adapts it to produce the proper effects. It might at first seem incredible that man and every thing at the surface of the earth is constantly subjected to the enormous pressure of fifteen pounds to every square inch of surface, but such it is well known is the fact; nor could the amount be essentially varied without producing injurious results. Was this pressure essentially increased the effect upon the delicate fibres and vessels of the systems, both of men and animals, would at once be injurious.

The whale is fitted to endure exceedingly great external pressure, but the amount which it can endure with impunity is limited, as frequently after it has descended to a great depth, upon rising to the surface, we are told it blows blood from the lungs and exhibits signs of great exhaustion. It is probable plants would also be affected injuriously by any great increase of pressure, though perhaps in a less degree than animals.

Any considerable increase of atmospheric pressure, and corresponding increase in the density of the air, would produce great inconvenience in causing many light bodies to rise and remain suspended in it, affecting the lungs and eyes in a manner not now to be realized, except perhaps in some degree by those who have been exposed to the fogs of Newfoundland, or the pillars of sand in the deserts of Africa. Was the pressure sufficient to produce a density at the surface equal to that of alcohol or water, nearly all vegetable and animal substances, unless they were fixed by some means to the spot, would rise from the surface; and the state of things that would ensue can perhaps be better depicted by the imagination than made the subject of grave description.

The temperature at which water and other liquids boil would also be raised by any increase of pressure. Under the existing atmospheric pressure water boils at 212° Fahrenheit, a circumstance which admirably adapts it to the wants of man. If the pressure of the atmosphere were only doubled, the boiling point of water (as determined by experiment) would be at 250° Fah.; and though it would still serve many important purposes, yet it would be less adapted to the wants of man than it now is. The steam engine would then be comparatively useless, because of the great expense of fuel that would be required to work it; and the danger of accidents from the high temperature of the water would be much greater. Very important effects would be produced in the arts in various ways, which, however, it might be difficult to determine in every case without experiment. The expense of distillation would of course be greatly increased, and in some cases where a substance has a high boiling point, it might be impracticable. On the other hand, inconveniences of an opposite character would result was the pressure of the atmosphere diminished. Smoke and dust, and other substances that now rise from the surface and pass away, might then incommode us by settling down; and the boiling points of water and other liquids would fall. If there was no atmospheric pressure, water would boil at 700 Fah., and alcohol at about 36°, so that neither could in summer be kept liquid without resorting to artificial means. Sulphuric ether, and some other liquids, would be known only as permanent gases.

It seems scarcely necessary to remark that in such a state of things man could not exist, even though air was not necessary to support respiration; and a great diminution of atmospheric pressure without its total removal would produce scarcely less disastrous effects. If the pressure, and consequently the density, of the atmosphere was essentially increased, combustion would be much more rapid than it now is; and the opposite effects and inconveniences would result were this pressure essentially diminished.

By the pressure of the atmosphere water and other liquids are made to rise in the common pump, and in the syphon, an effect which of course could not be produced were this pressure removed. Water may now be raised by the suction pump to the height of thirty-three or thirty-four feet, but was the atmospheric pressure reduced to one half, it could by this instrument be raised to only half this height, and so of any other proportion.

In speaking of the effects that would be produced by greater atmos pheric pressure than that which we at present witness, I have supposed a corresponding increase of density would attend any increase of pressure. This would necessarily be the case with our present atmosphere, and both the pressure and density evidently depend upon the quantity which surrounds the earth. If the quantity were greater than it is, the lower strata would of course be subjected to a greater pressure, by which the density would be increased in a corresponding ratio; and if the quantity were less, results the reverse of these would be produced.

But the atmosphere might evidently have been so constituted that its pressure would have been either greater or less than it now is, though its density might be the same, or its density might have been different under the existing pressure. Thus an atmosphere of hydrogen, with a pressure equal to that of the existing atmosphere, would be only about one fourteenth as dense; and an atmosphere of chlorine, under a pressure equal to that of the present atmosphere, would be about two and a half times as dense. But in either of these cases those effects which depend upon mere pressure would be precisely the same as pointed out above, and therefore require no separate elucidation.

3. The atmosphere produces very important and interesting effects in its relation to light. By the reflection of the sun's light by the atmosphere a faint luminousness is seen some time before he rises and after he sets, called twilight, which causes a gradual change in the morning from the darkness of night to the full light of day; and a gradual change in the reverse order in the evening. Was it not for the effects of the atmosphere, instead of the present gradual and pleasing change, we should be suddenly transferred from the darkness. of night to the full splendor of day, which could not but prove inju. rious, if not entirely destructive, to our eyes. I have said we should suddenly be transferred from the darkness of night to the splendor of day, which would indeed be the fact, but the splendor of day would be quite different from what it now is. The heavens would then at noon. day, instead of the beautifully and splendidly illuminated expanse, at present witnessed, present a surface of entire blackness, the sun appearing fixed in it like a burning jewel. And though the reflection from one substance to another might produce some diffusion of light

over the surface of the earth, nothing of the bright luminousness we now behold could then be known.

4. The purpose served by the atmosphere as a medium of communication by articulate sounds, is of immense importance. Sound, as is well known, is produced by undulations in the air, and but for its constant presence no verbal communication of individual with individual could be held. All intercourse must then be by gesture or other signs, and though man might still live in possession of all his corporeal and mental powers, it is almost certain that nothing like written language would ever be formed, or the advancement and improvement consequent upon it ever take place. But the Creator has not only given us those vocal organs so necessary to our physical and mental advancement, and the atmospheric fluid upon which they are to be exercised, but, in wonderful and admirable simplicity, he has provided that they may be brought into action, at the will of the individual, by the mere act of respiration! How evident in every part of this arrangement the wisdom and goodness of our adorable Creator!

Immediately connected with this is the whole subject of music, which is the source of so exquisite and refined pleasure. We can here enter into no lengthened disquisition upon this subject, but stop only to make a remark upon the almost innumerable variations of sound which the human ear is capable of distinguishing. Sounds differ from each other in pitch, in loudness, and in nameless other respects, which we have not terms in our language to designate, but which occasion the peculiarities in the voices of different persons, the sound of different musical instruments, &c. Supposing we can readily distinguish not less than two hundred and sixteen variations of pitch between the highest and lowest notes, and as many more in loudness, it is easy to show that the whole number of variations of sound the human ear is capable of distinguishing, cannot be less than two thousand millions.

5. The relation our atmosphere appears to sustain to the moisture which is always present in it, is scarcely less worthy of consideration. It was formerly supposed that there exists an actual affinity between atmospheric air and water, which causes a portion of it to be taken up in the air in the form of vapor, but this opinion is now generally relinquished, as it is found that in a given space, whether it be a vacuum or filled with air, the quantity of moisture that will rise de pends entirely upon the temperature. But here the wisdom of nature appears in the provision that moisture should be made to rise and diffuse itself among the particles of the air, while the latter presses upon the surface to an amount equal to fifteen pounds to the square inch. Had not the atmosphere possessed this property, it must alwayshave been in a state of perfect dryness; and, independent of the fact that the surface of the earth would never be moistened by the gentle dew or falling rain, it seems scarcely possible that men or animals could exist. Probably but a small portion of the whole moisture usually present in the atmosphere is ever expelled by ordinary artificial means, but even now, in rooms warmed by close stoves, it is often found necessary to contrive some special means to supply the atmosphere with the moisture of which it has been deprived. This is often done by placing a vessel of water upon the stove, which is rapidly evaporated by the heat, but in a much more delicate manner, by culti vating flowers in the room.

But if the atmosphere was incapable of receiving this watery vapor among its particles, far more important and decisive effects would follow. By the present arrangement of divine Providence, water from the great reservoirs in which it is collected rises in the air in the form of invisible vapor, which, after floating awhile in the air, is again condensed in dew, or falls in rain or snow upon the surface, giving rise to springs and rivers, which are designed to fertilize the earth and bless mankind. If the atmosphere then was destitute of this single property, there could be no such thing as rain or dew to moisten the earth, nor spring issuing from the valley, or river coursing its meandering way toward the level of the great ocean. Whatever may

at first have been the case, all the water on the surface of the globe must ere this have found the general level, there ever after to remain, unless its position should be changed by mechanical means. We are therefore probably correct in supposing that the destruction of this single property of atmospheric air would at once produce universal drought and barrenness, and ultimately the total extinction of animal and vegetable life.

6. By an increase of temperature air is expanded, and of course made to rise, yielding its place to be immediately reoccupied by other fresh portions. When it rises, being removed from a part of the pressure to which it was before subjected, it of course becomes still more rarified, and its temperature again reduced. By the heating influence of the sun's rays, in connection with the various reflections from the earth's surface, changes like these are constantly taking place on an immensely large scale, producing currents in the air called winds, in our latitude, in ever varying directions. Occasionally these currents of air are so violent as to produce great destruction to every thing ex. posed to their fury, but usually the gentle breezes that are given to fan creation may be classed among the greatest blessings of a benign Providence. If air was not affected in this manner by change of temperature, so far as we can perceive, no motion except that produced by mechanical means could ever take place; but the rough boreas and gentle zephyr would be alike unknown, and the whole atmosphere would always present an unvaried, stagnant calm. The sail of the tall ship and little nautilus would be alike useless, nor could the benefits and improvement resulting from the use of the former, or the pleasure derived from the contemplation of the latter, ever be realized. All the injurious effects that would result cannot probably be seen, but enough is evident to satisfy us that no improvement in respect to this property of air could be made.

In consequence of this property, air that has been rendered unfit for farther use by combustion or respiration, in consequence of the heat that has been communicated to it, immediately rises and passes away, even in the open air, and produces in chimneys and stoves those currents that convey away the smoke and other hurtful exhalations.

7. The atmosphere is also made the theatre of many electrical phenomena, the importance of which in the economy of nature, in consequence of the extremely subtle nature of the electric fluid, is not probably fully understood. Air in a dry state is one of the best nonconductors of electricity, and hence this fluid does not usually traverse it silently, but accumulates till it acquires sufficient intensity to pass