Indeed, if we examine the most ancient of histories, we find one great fact at the base of all their philosophies. Moses connects darkness with a void and formless earth, and light with the creation of harmony and life. Menis sings of a fearful world by “many formed darkness encircled,” and links the idea of a “life-breathing divinity” with the awakening of light upon created things. The Egyptian Isis, the Grecian Apollo, who,
The Lord of boundless light
Ascending calm o’er the empyrean sails,
And with ten-thousand beams his awful beauty veils,
the fire-worshipper of the Persian hills and the sun-god of the Peruvian mountains, exhibit, through time and space, the full consciousness of man to the influences of solar light and heat upon the organic creations of which he is himself the chief exemplar.
The investigations of modern philosophers have extended these influences to the inorganic masses which constitute the Planet Earth:—and we now know that the physical forces, ever active in determining the chemical condition and the electrical relations of matter, are directly influenced by the solar radiations.
Few things within the range of our inquiry are more striking than the phenomena of calorific radiation and absorption. They display so perfectly the most refined system of order, and exhibit so strikingly the admirable adaptation of every formation to its particular conditions, and for its part in the great economy of being, that they claim most strongly the study of all who would seek to discover a poetry in the inferences of science.
Owing to the nature of our atmosphere, we are protected from the influence of the full flood of solar heat. The absorption of caloric by the air has been calculated at about one-fifth of the whole in passing through a column of 6,000 feet. This estimate is, of course, made near the earth’s surface; but we are enabled, knowing the increasing rarity of the upper regions of our gaseous envelope in which the absorption is constantly diminishing, to prove, that about one-third of the solar heat is lost by vertical transmission through the whole extent of our atmosphere.[47]
Experience has proved that the conditions of the sun’s rays are not always the same; and there are few persons who have not observed that a more than usual scorching influence prevails under some atmospheric circumstances. This is also evidenced in the effects produced on the foliage of trees, which, though often attributed to electricity, is evidently due to heat. An examination of the solar radiations, as exhibited in the prismatic spectrum, has proved the existence of a class of heat rays, which manifest themselves by a very peculiar deoxidizing power quite independent of their caloric properties, to which the name of parathermic rays has been given.[48] We are protected from the severe effects of these rays by the ordinary state of the medium through which the solar heat passes. Our atmosphere is a mixture of gases and aqueous vapour; and it has been found, as already stated, that even a thin film of water, however transparent, prevents the passage of many calorific radiations, and the rays retarded are, for the most part, of that class which have this peculiar scorching power. The air is, in this way, the great equaliser of the solar heat, rendering the earth agreeable to all animals, who, but for this peculiar absorbent medium, would have to endure, even in our temperate clime, the burning rays of a more than African sun.