Page:Popular Science Monthly Volume 31.djvu/534

518 It suggests to us this primitive energy of separation as the probable source of such light and heat in suns and stars as we now know them. It posits for us our own planet as an orb gathered in from the original cloud-mass, with outer surface cooled and corrugated, and with two great envelopes, atmospheric and oceanic, gaseous and liquid, still floating or precipitated around its denser core. It teaches us how the hard crust of the hot central mass has been uplifted here into elevated table-land or depressed there into hollow ocean-bed. By the aid of its newest instrument, meteorology, it lets us see how incident solar energy, raising clouds and causing rainfall, with its attendant phenomena of drainage and rivers, has carved and denuded the upheaved masses into infinite variety of hill and valley. It shows us how sediment, thus gathered by streams on the bed of the sea, is pushed up once more by volcanic power or lateral pressure into Alpine chains and massive continents, and how these in their turn have been worn down by the long-continued bombardment of aqueous or aërial action into mere stumps or relics of their primitive magnitude. It puts before us life as an ultimate result of solar energy falling on the watery and gaseous shell of such a solidified planet. It suggests to us how light, acting chemically on the leaves or fronds or cells of the green herb, stores up in them carbohydrates, rich in potential energy, which animals afterward use up as food, or man utilizes as coal in his grates and his locomotives. It exhibits to us the animal organism as essentially a food-engine in whose recesses solar energy, stored as potential by the plant, is once more let loose by slow combustion in the kinetic form as heat and motion. It enables us to regard the body as a machine in which stomach and lungs stand for furnace and boiler, the muscles for cylinder, piston, and wheels, and the nervous system for an automatic valve-gear. It traces for us from small beginnings the gradual growth of limb and organ, of flower, fruit, and seed, of sense and intellect. With the simple key of survival of the fittest it unlocks for us the secret of organic diversity and universal adaptation. It reconstructs for us from obscure half-hints the origin of man; the earliest stages of human history; the rise of speech, of arts, of societies, of religion. It unifies and organizes all our concepts of the whole consistent system of Nature, and sets before our eyes the comprehensive and glorious idea of a cosmos which is one and the same throughout, in sun and star and world and atom, in light and heat and life and mechanism, in herb and tree and man and animal, in body, soul, and spirit, mind and matter. Almost all that is most vital and essential in this conception of our illimitable dwelling-place, the last half-century has built up for us unaided.—Fortnightly Review.