Does the Air Ever Get Used Up?
We may say that, in a sense, a great deal of the air has already been used up: for we know that by far the greater part of all the surface of the earth, including all the water of the seas, is already burned, and so has used up a great deal of the oxygen of the air. That happened a long time ago, however, before there were any living creatures. on the earth.
The air is constantly being used now - or, rather, the oxygen of it is being used - in the breathing of all living creatures: while the nitrogen of the air is being used by certain microbes, and now also by men themselves, who use electricity for this purpose; and, thirdly, green plants use the carbon dioxide of the air, upon which they feed.
Yet the air does not get used up as far as any of these gases are concerned. There must be compensation of some kind going on. There is compensation in regard to the oxygen because green plants everywhere in the sunlight are giving off to the air a great deal of oxygen - perhaps enough to make up for what they take in by breathing, and possibly also enough to make up for what animals and men take in by breathing.
As for the nitrogen that is used, we can easily show that that is compensated for; for when animals and plants die, their bodies decompose, and most of the nitrogen they contain, which they originally got from the air, is given back to the air. Lastly, the carbon dioxide taken from the air by plants is compensated for by the carbon dioxide which all living creatures give out to the air when they breathe.
Are the Clouds Part of the Earth or Do They Go Around With It?
Certainly the clouds are part of the earth. We sometimes forget that we do not really live on the outside of the earth at all, but only at the bottom of its outside layer, which we call the air or, in technical language, the atmosphere. That outside layer, and all it contains, such as the clouds, is as much part of the earth as the mountains or the oceans are. It is true that, from our point of view, we may think of the air as something laid on outside us to serve as a parasol by day and a blanket by night, as it does; but then our point of view depends on where we are.
The clouds are part of the earth and go round with it, as does the atmosphere in which the clouds hang. No doubt it is true that, as the earth spins, the air rather tends to drag behind; and high clouds will do this also. But, in general, the air and the clouds certainly spin round with the earth.
