OCR Text |
Show 158 AIR. moving differently or at rest, by means of which we can know and judge of the motion. We can treat only of what we know; and thus every attempt to expl ain the principles or agencies which have been noticed must be made through the medium of those matters in which their effects are displayed. Now, however, we come to a real substance, or perhaps, more correctly, to a state in which ~orne substances generally, and all substances at times, exist. That substance is AIR, the lightest, the softest, the :fleetest, the most gentle, and the most obedient of all material things, of which the human senses can have any know ledge. The common atmosphere which we breathe, and without which we could not possibly live, is the type, and most familiar instance of air. But it is the state, and not the substance,. that is aerial. Besides water, and other foreign substances, of which it always contains some portion, however small, the common air, or atmosphere, consists of two ingredients-oxygen and nitrogen. The first of these forms part of water, of every animal and every vegetable, and of many mineral or earthy substances ; and the latter forms part of every animal, and of some vegetables-of caoutchouc, or Indian rubber, for instance, and of course of the trees whose juice consolidates into that substance. But though the atmospheric. compound of oxy~en and nitrogen be the type, and, to popular observatiOn, the example of air, yet air may mean any thing, or all things ; because all things, or the elements of which all things are composed, may exist in the state of air. The most accurate definition of air is, · "matter subdued by heat,"-so overcome by the tendency to motion which heat imparts, that it has no cohesion, and none of the common properties of matter, excepting gravitation-the property which matter never loses, or can lose, while it exists. No matter what the substance be which is in the state of air; be it 6ydrogen, which when in a state of air is the lightest WHAT AIR IS. 159 of _known substances, and on that account used for filhng balloons, which, because of their lio-htness rise in the air and carry up men and their inst~ment~ of obs_ervation ;_or be it gold or platinum, which, when m the sohd state, are the heaviest of known subs_tances, sti_ll if it be_ in the state of air, all its properties, as sohd or as liquid matter, are subdued and suspended by heat, when it is in the state of air ~ excepting gravitation or weight. The direct actio~ of. that is also suspended, and a heavy metal may, by hem&' reduced to the state of air or vapour, be made to float m the atmosphere, and to pass upward rather than downward. But that is owing to the dispersion of the minute part.s o~ it thro~gh much more space than they occupied m the solid or the liquid form. Could all those_ scatter~d particles be collected, they would at all tunes ~mgh exactly the same ; and if they were_ made agm_n t? occupy just the same space as ~he sohd ~r t_he hqmd, all the properties of the sohd ?r th~ hqmd would return, and it would be the ~arne Identical substance that it was before the action of heat turned it into air. In th~ act_ions or changes that take place in nature (for _ac~wn Is but another name for change) the state of au IS of the utmost consequence; and it is highly probable, nay, absolutely certain, that without that stat~ t~ere would be no action whatev~r. The state of au Is the ~nd of every thing old and the beginning of_ every thi?g n~w. The ma~ter of which any thmg-:-all thmgs, IS composed Is altogether indestructible. by a~y natura~ cause; and, therefore, the only warm whwh anythmgcan be destroyed is by the destruc~wn or complete su~pension of all its peculiar nropert:Ies, by the conversiOn of it into air throuo-h the acti_on ~f ~eat. While it retains all the form~r pro~ertles, It IS the former substance ; and while it retams sor_n~ of them, after others have ceased to be apparent, It Is the ruin of the former substance; but when the whole of the former properties are suspended, and the substance (still identically the same |