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water was also gathered up into the atmosphere, and suspended there in clouds, which became as the garment thereof, (Job xxxviii. 9:) thus the waters were divided from the waters, and the means provided by which the earth might be continually refreshed by the early and the latter rain ; for the clouds became from this day God's appointed reservoir of the rain and snows, which in due season should come and water the earth, to make it bring forth and bud, giving seed to the sower and bread to the eater. (Isa. lv.) But the subject of the atmosphere is so full of interest, both in its formation and various properties, that we must not hastily pass away from it; and therefore I will endeavour to inform your young minds as to these two particulars. And here I must of necessity use some scientific terms; but though I know such hard names at first sight seem difficult to remember, yet it is manifest, that the language of science, if not the most beautiful is the most expressive ; for every word carries within itself its own signification; whilst, therefore, dear children, I will seek to avoid an unnecessary use of these terms, I have little doubt but we shall soon agree that they are even easier to retain than words in common use.

First, then, let me explain to you the formation of the atmosphere, or the air, with which we are surrounded. Naturalists-that is, men of science who have made these subjects their especial studyhave ascertained that the air is composed of two principal gases, or elastic fluids, which have been named by them, Oxygen and Nitrogen., The first is emphatically the sustainer of life, animal and vegetable ;

the second has no such power, and so has been also called azote, that is, without life : but as the oxygen would be too active alone, it is diluted with nitrogen, as water dilutes wine. The relative proportions are,—twenty parts oxygen, eighty nitrogen. In addition to these, there is also a small proportion of carbonic acid gas, and some hydrogen, but only in the proportion of one part to ninety-nine. The height of the atmosphere, it is calculated, does not exceed fifty miles,* expanding all the while as it ascends; and at that height it becomes so rarified that it cannot be respired: indeed, Æronauts, or air sailors, as the word means, who have never ascended beyond 5} miles, have even then found great difficulty in breathing; and on account of the atmosphere being so much lighter, they have in many cases bled profusely from the nose and mouth ;-but though the air thus expands, yet the parts of which it is composed necer in the least degree vary their relative proportions. One traveller brought some air down from Chimborasso, the highest of the Andes, (ihat amazing range of mountains which I have so often described to you,) and compared it with some taken from the lowest valley beneath; but the proportions were the

Others, again, have examined the atmosphere of the pestilent marshes near Rome; but in this case also there was not the slightest variation. If death was there, it arose not from the absence of the cital oxygen, (that was there true to its proportions,) but from some principle of too subtle a nature to be detected by chemical analysis. Indeed,

• See Appendix.

same.

the infectious atmosphere of an hospital has been examined with great care, even when its ill odour was intolerable, but no perceptible difference could be detected.

Having thus far explained the nature of our atmosphere, I will now endeavour to make plain to you its properties.

The first great property of the atmosphere, as I have before remarked, is to sustain animal and vegetable life. The absence of it from one or the other would cause instant death. This has been abundantly proved by experiment: for place either an animal or vegetable in any vessel air tight, and then exhaust the air, and life is at once destroyed. But, not only would death instantly ensue, if the air were taken from us; but if it ever caried its proportions, all would be in misery: and yet near 6000 years have run out since its formation; and the little child just born inhales it with the same freedom as the first offspring of man. But, let us suppose, for instance, that we inhaled nothing but the pure oxygen, or vital air; after a very little, the lungs would become so excited, that nature could not long sustain the unnatural stifling fulness; and if, on the contrary, we inhaled only nitrogen, we should die; for it has been ascertained by experiment, that animals put into a vessel filled only with nitrogen, die instantly. And then, if the PROPORTIONS WERE DIFFERENT :-the oxygen prevailing, we should be in perpetual excitement, and rendered perfectly miserable; the nitrogen prevailing, we should be continually panting for breath, and at last faint away and die. But the air,

measured and proportioned by the hand of infinite tenderness and compassion, the simple act of respiration, which most men enjoy, is in itself a continual pleasure; but this we seldom think about, until, from bodily infirmity, or from being shut up in a little room with a great number of people, like the poor sufferers in the Black-hole at Calcutta, or walking through a dense fog, or passing some Lime Kilns, (from which carbonic acid gas is given off abundantly,) as we did the other day, we learn its value by the painful contrast.

The following beautiful remark on the action of the oxygen I know will interest you:

“ Animals cannot live without oxygen. By ineans of this gas, a change which the eye can detect is produced in the blood,—the dark coloured fluid of the veins combined with oxygen becomes the bright scarlet blood of the arteries, and in this blood is the life.”

But not only does man inhale the atmospheric air, but also the whole of vegetable life depends every moment on it, but with this remarkable difference, that whilst man and the animal retain the oxygen, but exhale or give out the carbonic acid gas, the grass and shrubs and trees care not for the oxygen, but greedily drink in the carbonic acid gas, which is so prejudicial to man. It is this that makes a walk in the country so healthy, as well as pleasant. At night, however, this is reversed: then the vegetable demands its share of the rital air, and gives out carbon. Thus, while plants, or branches of shrubs in water, are most useful in a sick room BY DAY, they are very prejudicial

BY NIGHT. I might write you a great deal more on this subject; but I must pass on now to consider the second great property of the atmosphere, as the great reservoir of rain and snow. Now, suppose you read in 1 Kings xviii. 2–5, there you see what would be the state of the land if there was no such reservoir as I have mentioned; for then God withheld the rain in judgment, and all things perished. The accounts from Australia, also, received in our last letters, give ample proof of the same thing in our day. But this is the exception to the general rule; for since the beautiful Bow has been seen in the cloud, seed-time and harvest have not failed. But here I imagine a difficulty that would be quickly proposed if I were sitting by you—“Do not the clouds ever get emptied ? I should have thought that a few such nights as we had about a month since would have emptied ALL the clouds." The remark, dear children, is not at all a foolish one; for the clouds of course would empty themselves, but for one thing. “Now what is that one thing ?” I suppose you are all curious to inquire: and I answer,—it is the principle of evaporation, by which, in infinitely fine particles, lighter than the air near the earth,* there ascends up to the clouds, and this continually, an amazing body of water; and so by this invisible agency they are kept always supplied. And here I place before you, dear children, two calculations of great interest :-first, it is estimated, that in England and Wales alone, rain falls yearly to the extent of 100,000 millions of tons (and so I

See Appendix.

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