We ask for its “object” perhaps with an unconscious assumption that the whole must have been in some way provided to subserve our wants; but there is not as yet the slightest evidence connecting its existence with any human need or purpose, and as yet we have no knowledge that, in this sense, it exists to any “end” at all. “As the thought of man is widened with the process of the suns,” let us hope that we shall one day know more.
III.
THE SUN’S ENERGY.
“It is indeed,” says good Bishop Berkeley, “an opinion strangely prevailing amongst men that ... all sensible objects have an existence ... distinct from their being perceived by the understanding. But ... some truths there are, so near and obvious to the mind, that a man need only open his eyes to see them. Such I take this important one to be, namely, that all the choir of heaven and furniture of the earth—in a word, all those bodies which compose the mighty frame of the world—have not any subsistence without a mind.”
We are not going to take the reader along “the high priori road” of metaphysics, but only to speak of certain accepted conclusions of modern experimental physics, which do not themselves, indeed, justify all of Berkeley’s language, but to which these words of the author of “A New Theory of Vision” seem to be a not unfit prelude.
When we see a rose-leaf, we see with it what we call a color, and we are apt to think it is in the rose. But the color is in us, for it is a sensation which something coming from the sun excites in the eye; so that if the rose-leaf were still there, there would be no color unless there were an eye to receive and a brain to interpret the sensation. Every color that is lovely in the rainbow or the flower, every hue that is vivid in a ribbon or sombre in the grave harmonies of some old Persian rug, the metallic lustre of the humming-bird or the sober imperial yellow of precious china,—all these have no existence as color apart from the seeing eye, and all have their fount and origin in the sun itself.
“Color” and “light,” then, are not, properly speaking, external things, but names given to the sensations caused by an uncomprehended something radiated from the sun, when this falls on our eyes. If this very same something falls on our face, it produces another kind of sensation, which we call “heat,” or if it falls on a thermometer it makes it rise; while if it rests long on the face it will produce yet another effect, “chemical action,” for it will tan the cheek, producing a chemical change there; or it will do the like work more promptly if it meet a photographic plate. If we bear in mind that it is the identically same thing (whatever that is) which produces all these diverse effects, we see, some of us perhaps for the first time, that “color,” “light,” “radiant heat,” “actinism,” etc., are only names given to the diverse effects of some thing, not things themselves; so that, for instance, all the splendor of color in the visible world exists only in the eye that sees it. The reader must not suppose that he is here being asked to entertain any metaphysical subtlety. We are considering a fact almost universally accepted within the last few years by physicists, who now generally admit the existence of a something coming from the sun, which is not itself light, heat, or chemical action, but of which these are effects. When we give this unknown thing a name, we call it “radiant energy.”
How it crosses the void of space we cannot be properly said to know, but all the phenomena lead us to think it is in the form of motion in some medium,—somewhat (to use an imperfect analogy) like the transmission through the air of the vibrations which will cause sound when they reach an ear. This, at any rate, is certain, that there is an action of some sort incessantly going on between us and the sun, which enables us to experience the effects of light and heat. We assume it to be a particular mode of vibration; but whatever it is, it is repeated with incomprehensible rapidity. Experiments recently made by the writer show that the slower heat vibrations which reach us from the sun succeed each other nearly 100,000,000,000,000 times in a single second, while those which make us see, have long been known to be more rapid still. These pass outward from the sun in every direction, in ever-widening spheres; and in them, so far as we know, lies the potency of life for the planet upon whose surface they fall.
Did the reader ever consider that next to the mystery of gravitation, which draws all things on the earth’s surface down, comes that mystery—not seen to be one because so familiar—of the occult force in the sunbeams which lifts things up? The incomprehensible energy of the sunbeam brought the carbon out of the air, put it together in the weed or the plant, and lifted each tree-trunk above the soil. The soil did not lift it, any more than the soil in Broadway lifted the spire of Trinity. Men brought stones there in wagons to build the church, and the sun brought the materials in its own way, and built up alike the slender shaft that sustains the grass blade and the column of the pine. If the tree or the spire fell, it would require a certain amount of work of men or horses or engines to set it up again. So much actual work, at least, the sun did in the original building; and if we consider the number of trees in the forest, we see that this alone is something great. But besides this, the sun locked up in each tree a store of energy thousands of times greater than that which was spent in merely lifting the trunk from the ground, as we may see by unlocking it again, when we burn the tree under the boiler of an engine; for it will develop a power equal to the lifting of thousands of its kind, if we choose to employ it in this way. This is so true, that the tree may fall, and turn to coal in the soil, and still keep this energy imprisoned in it,—keep it for millions of years, till the black lump under the furnace gives out, in the whirling spindles of the factory or the turning wheel of the steamboat, the energy gathered in the sunshine of the primeval world.
The most active rays in building up plant-life are said to be the yellow and orange, though Nature’s fondness for green everywhere is probably justified by some special utility. At any rate, the action of these solar rays is to decompose the products of combustion, to set free the oxygen, and to fix the carbon in the plant. Perhaps these words do not convey a definite meaning to the reader, but it is to be hoped they will, for the statement they imply is wonderful enough. Swift’s philosopher at Laputa, who had a project for extracting sunbeams out of cucumbers, was wiser than his author knew; for cucumbers, like other vegetables, are now found to be really in large part put together by sunbeams, and sunbeams, or what is scarcely distinguishable from such, could with our present scientific knowledge be extracted from cucumbers again, only the process would be too expensive to pay. The sunbeam, however, does what our wisest chemistry cannot do: it takes the burned out ashes and makes them anew into green wood; it takes the close and breathed out air, and makes it sweet and fit to breathe by means of the plant, whose food is the same as our poison. With the aid of sunlight a lily would thrive on the deadly atmosphere of the “black hole of Calcutta;” for this bane to us, we repeat, is vital air to the plant, which breathes it in through all its pores, bringing it into contact with the chlorophyl, its green blood, which is to it what the red blood is to us; doing almost everything, however, by means of the sun ray, for if this be lacking, the oxygen is no longer set free or the carbon retained, and the plant dies. This too brief statement must answer instead of a fuller description of how the sun’s energy builds up the vegetable world.