agitation, motion, mixing, and circulation, the airy covering of the globe is kept in that state which the well-being of the organic world requires. Every breath we draw, every fire we kindle, every blade of grass that grows or decays, every blaze that shines and burns adds something that is noxious, or takes something that is healthful away from the surrounding air. Diligent, therefore, in their offices must the agents be which have been appointed to maintain the chemical status of the atmosphere, to preserve its proportions, to adjust its ingredients, and to keep them in that state of admixture best calculated to fit it for its purposes.
237. Experiments by the French Academy.—Several years ago the French Academy sent out bottles and caused specimens of air from various parts of the world to be collected and brought home to be analyzed. The nicest tests which the most skilful chemists could apply were incapable of detecting any, the slightest, difference as to ingredients in the specimens from either side of the equator; so thorough in the performance of their office are these agents. Nevertheless, there are a great many more demands on the atmosphere by the organic world for pabulum in one hemisphere than in the other; and consequently a great many more inequalities for these agents to restore in one than in the other. Of the two, the land of our hemisphere most teems with life, and here the atmosphere is most taxed. Here the hearthstone of the human family has been laid. Here, with our fires in winter and our crops in summer, with our work-shops, steam-engines, and fiery furnaces going night and day—with the ceaseless and almost limitless demands which the animal and vegetable kingdoms are making upon the air overhead, we cannot detect the slightest difference between atmospherical ingredients in different hemispheres; and yet, notwithstanding the compensations and adjustments between the two kingdoms of the organic world, there are almost in every neighbourhood causes at work which would produce a difference were it not for these ascending and descending columns of air;—were it not for the obedient winds,—for this benign system of circulation,—these little cogs and ratchets which have been provided for its perfect working. The study of its mechanism is good and wholesome in its influences, and the contemplation of it well calculated to excite in the bosom of right-minded philosophers the deepest and best of emotions.
238. How supplies of fresh air are brought down from the upper
