I cannot dismiss the system of the Apollonian without setting in contrast with it the discoveries of modern science respecting the relations of the air. Toward the world of life it stands in a position of wonderful interest. Decomposed into its constituents by the skill of chemistry, it is no longer looked upon as a homogeneous body; its ingredients have not only been separated, but the functions they discharge have been ascertained. From one of these, carbonic acid, all the various forms of plants arise; that substance being decomposed by the rays of the sun, and furnishing to vegetables carbon, their chief solid ingredient. All those beautifully diversified organic productions, from the mosses of the icy regions to the palms characteristic of the landscapes of the tropics--all those we cast away as worthless weeds, and those for the obtaining of which we expend the sweat of our brow--all, without any exception, are obtained from the atmosphere by the influence of the sun. And since without plants the life of animals could not be maintained, they constitute the means by which the aërial material, vivified, as it may be said, by the rays of the sun, is conveyed even into the composition of man himself. As food, they serve to repair the waste of the body necessarily occasioned in the acts of moving and thinking. For a time, therefore, these ingredients, once a part of the structure of plants, enter as essential constituents in the structure of animals. Yet it is only in a momentary way, for the essential condition of animal activity is that there shall be unceasing interstitial death; not a finger can be lifted without the waste of muscular material; not a thought arise without the destruction of cerebral substance. From the animal system the products of decay are forthwith removed, often by mechanisms of the most exquisite construction; but their uses are not ended, for sooner or later they find their way back again into the air, and again serve for the origination of plants. It is needless to trace these changes in all their details; the same order or cycle of progress holds good for the water, the ammonia; they pass from the inorganic to the living state, and back to the inorganic again; now the same particle is found in the air next aiding in the composition of a plant, then in the body of an animal, and back in the air once more. In this perpetual revolution material particles run, the dominating influence determining and controlling their movement being in that great centre of our system, the sun. From him, in the summer days, plants receive, and, as it were, store up that warmth which, at a subsequent time, is to reappear in the glow of health of man, or to be rekindled in the blush of shame, or to consume in the burning fever. Nor is there any limit of time. The heat we derive from the combustion of stubble came from the sun as it were only yesterday; but that with which we moderate the rigour of winter