Nothing is more interesting than those general laws by which God preserves the order of the world. If we had a complete knowledge of all the wonderful contrivances that surround us, we should be filled with admiration and awe: to contemplate those with which we are acquainted, is the highest of intellectual pleasures.
One of these contrivances may be made intelligible even to those who have no acquaintance with Natural Philosophy.
The Air is made up of two different gases, or airs, mixed together in a particular proportion. Of these, one (oxygen), which we will call life-air, is necessary for the support of men and all other animals, which would die without it; neither could any thing burn without the help of this life-air Since, then, a vast quantity of it is consumed every hour, how is the supply kept up? How is it that the stock of life-air is still sufficient for us, and our fires and candles?
Now, besides these two gases, there is also present in the atmosphere another gas, called carbonic acid, which is made up of carbon and life-air. The name will he unknown to many, but all are well acquainted with the thing: it is what gives spirit to ale, wine, &c., and even to water, which is insipid after boiling, from the loss of its carbonic acid.
This carbonic acid is produced by the breathing of animals, and the putrefaction of animal and vegetable substances. Now, this constant supply must be got rid of, or it would kill us; and it is got rid of thus: all vegetablesgrass, herbs, trees, &c.suck in this carbonic acid during the day; nourish themselves with the carbon, and give back the life-air that was combined with it. In the night, they do the reverse; but still, taking a whole day, they lessen the quantity of carbonic acid gas, and furnish the atmosphere with that supply of life-air, which is necessary for the existence of the animal creation.