5 i8 THE POPULAR SCIENCE MONTHLY. 



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 origi- 

 nal 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 aerial 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 after- 

 ward 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 auto- 

 matic valve-gear. It traces for us from small beginnings the gradual 

 growth of limb and organ, of flower, fruit, and seed, of sense and in- 

 tellect. With the simple key of survival of the fittest it unlocks for 

 us the secret of organic diversity and universal adaptation. It recon- 

 structs 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 con- 

 sistent 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-cent- 

 ury has built up for us unaided. Fortnightly Hevlew. 



