The few details which we have thrown together, bearing upon the natural light of our planet, derived from the sun, will suggest to the mind of the Christian those apt comparisons, of the broad light of day to the light of the gospel, transmitted to our souls from the Sun of righteousness. Till illuminated from above, man wanders in spiritual darkness; he sees neither the dangers that encompass him, nor the road by which he should go; he may have the light of nature and the light of science within him, but in spiritual affairs he is blind, and will be chosen only by the blind as a leader. Let, however, the light of revelation begin but to dawn upon him, and he learns to discover more and more clearly his real position, his true character, and the impossibility of his finding acceptance before God upon his own merits. He feels himself to be a sinful creature, and is led to rest upon the merits and atonement of the Son of God, who died for our sins, and rose again for our justification. Thus enlightened, he receives strength to pursue his journey to that bright and glorious kingdom of which God himself is the Sun, and where there shall no more be night, where "everlasting day abides," and all is glory and refulgence.
4. Its Temperature.—Heat and light are distinct from each other, though in many cases one accompanies the other, and is produced by the same cause, as, for instance, by combustion, electricity, percussion, the sudden condensation of air, etc. Heat without light, however, is developed by the physical or chemical changes of bodies, as by the condensation of steam, and the admixture of water with sulphuric acid. It results, moreover, from the vital and mysterious operations which are constantly taking place in organic beings, and especially in the classes of mammalia and birds. But the great source of heat—that upon which the temperature of our atmosphere mainly depends—is produced by the influence of the solar rays.
There is, indeed, heat in the body of the globe itself; to say nothing of volcanoes, we may state, that the deeper we penetrate into the earth, the higher does its temperature become—a circumstance which has led many philosophers to infer, that the centre of our globe is in a state of incandescence. It is not here that we ought to moot this theory, neither shall we enter into any speculations relative to the intrinsic nature of heat; like light, it is a mysterious agent or product, imponderable, yet subject to certain laws—laws which belong to a branch of philosophy into which it is not now our province to enter.
It may, however, be permitted us to state a few simple facts relative to the atmospheric temperature of our globe, and the adaptation of organic beings to the different degrees of heat within the inter-tropics, in the temperate and in the polar latitudes. Climate varies not only according to latitude, but also according to elevation, the relative proportions of land and water, the nature of the surface of the land, the extent of forests, etc. An island, for example, like England, surrounded by the sea, destitute of mountains of vast elevation, or of extensive morasses or forests, though lower in atmospheric temperature during the summer months than the parallel portions of the continent, has a milder atmospheric temperature during winter. The cold of North America during winter is greater than in the same parallels of latitude in the old world. Canada, for example, lies parallel to the northern half of Spain and France, (between 40° and 50° N. lat.) The severity of a Canadian winter is well known. At Quebec, the summer is that of Paris, the winter that of St. Petersburg. At New York, the summer is that of Rome, the winter that of Copenhagen. The same observations apply to the eastern portions of Asia. At Pekin, the scorching heat of summer is greater than at Cairo, while the winters are as rigorous as at Upsal.
To the different climates of the globe certain plants and animals are especially adapted; organic existence ranges from the poles to the equator. How varied, how multitudinous, how wonderful, are the forms and structures of organic creation, from the moss or lichen, which creeps upon the surface of the rock, to the towering palm or gigantic oak—from the microscopic animalcule or puny insect, to the ponderous elephant or enormous whale! But, as we have said, every distinct region has, in a general sense, its own flora and its own fauna. It is in tropical countries, beneath a fervid sun, that vegetation presents us with its utmost magnificence. There we see forests of evergreen trees, palms, and arborescent ferns—there bloom flowers of gorgeous hue, and luscious scent—there ripen fruits of most exquisite flavour, attractive both to the sight and the taste.
It is there, too, that the elephant, the hippopotamus, and the rhinoceros, the largest of terrestrial quadrupeds, roam the plain, or wander in the dense forest; there are the birds conspicuous for the gorgeous splendour of their metallic colours, and the insects for their singular forms, their lovely painting, or dazzling effulgence. Receding from the inter-tropics, we find vegetation on a less magnificent scale; the trees are for the most part deciduous, various species of corn are cultivated, the meadows are clothed with grass, and the vine and the olive flourish. Beautiful are the flowers, richly tinted are the insects; some few birds are splendid, but there are no sun birds, no humming birds, no birds of paradise. Receding further, we come to the extreme limits of the vine, and pass from temperate to colder latitudes, latitudes in which pines and firs form woods and forests, in which a scanty flora greets a tardy sun, in which the animals are covered with fur, increasing in thickness on the approach of winter. Beyond this territory the arctic regions open upon us. Yet even here vegetable and animal life meet us; but the species are few in number: the reindeer, the leming, the white hare, the musk ox, the polar bear, and arctic fox, are among the most remarkable. The birds are chiefly piscivorous, and all are migratory, passing southwards on the approach of winter. Coarse herbage, lichens, and mosses, vegetate during the fleeting summer, and lie buried beneath the snow during the winter. Yet are these animals and plants as well adapted for their dreary realms of snow and ice, as are the animals and plants of the rich inter-tropics for their luxuriant region. Take the elephant, the hippopotamus, the bird of paradise, or the glittering boa constrictor to Greenland, and they perish; take thither the graceful palm, palmetto, or pandanus, and they cease even to struggle for life. On the contrary, transport the polar bear and the reindeer to the torrid plains of the inter-tropics, and their fate is sealed. The hardy plants, indeed, which endure the arctic regions, are, in many instances, at least identical with those that flourish in more temperate latitudes, but they are not to be found in the low sultry plains of the inter-tropics. They constitute the outskirts of northern vegetation.
The inter-tropical, the temperate, and the high northern regions of the globe, are characterised, then, by their own flora and fauna; but there is a distribution of organic life exclusive of latitude, which cannot but claim the attention of the naturalist. For example, the marsupial animals are distributed between Australia and central and southern America; but the American forms, very few in number, are essentially distinct from those of Australia. Again, it is to the warmer regions of the old world that the larger pachydermatous animals are confined, such as several species of rhinoceros, the hippopotamus, a tapir, two species of elephant, wild equine animals, as the dziggetai, wild ass, quagga, zebra, etc., and various species of wild hog. The living indigenous pachydermata of America consist of two species of tapir, and two of peccary. On the contrary, America is rich in the edentata, namely, sloths, ant-eaters, armadilloes, etc. The pangolins, however, (manis,) are found only in the warmer parts of the old world, and the aard-vark (orycteropus) is a native of South Africa. We might enlarge greatly upon these observations, and extend them to birds and reptiles, etc., were it our design to enter upon the question; we shall only add, that in all regions animals are expressly suited to the climate of the countries in which they respectively live; they are constituted for the endurance either of heat or of cold, for self-protection against all extremes of atmospheric temperature, and for the enjoyment of existence, some under the equinoctial line, others within the arctic circle.
The foregoing observations do not apply to the human race. Man was ordained to replenish the earth; hence the pliability and energy of his physical constitution, which enables him to endure the heat of the inter-tropics, and the cold of Lapland or Nova Zembla—to dwell in the deep valley or on the lofty mountain. When we say this, we look at man as a species; we do not apply our remarks to individuals, or, in other words, we do not assert that a Samoiede would enjoy the heat of Ceylon or Sumatra, or that the Ceylonese would endure the rigours of arctic Siberia; we only mean, that the fact of hot and cold climates being inhabited by our race, proves that the physical condition of man can accommodate itself to every extreme of natural temperature upon our globe. It is true, that as a general rule man modifies his food, his clothing, and even the nature of his habitation, according to the temperature and products of the climate. The Laplander clothes his body in warm furs, the Ceylonese in a scanty vesture of thin cotton. Yet the wild Indians of some parts of North America, and the natives of the dreary regions of Patagonia, are but loosely defended from the severity of the cold, either as it respects dress or their huts. The Scottish Highlander of the olden time, wrapped in his tartan, could sleep on the heather of the mountain side during a bitter sleety night without injury. After all, however, in the arctic regions the maintenance of life is a struggle; the depressing influences of cold, cheerless skies, and scanty food, tend to render the powers of the mind and the bodily frame alike stunted and undeveloped. Nature here holds out the means of life with a niggard hand, and it is from the sea principally that the supply of food and other necessaries are obtained.
On the other hand, within the tropics the means of existence are lavishly bestowed, the stimulus of animal food is not required, while the earth yields its vegetable productions in abundance; but in these regions, no strong motive stimulating to active exertion, the mental powers become enfeebled, and all those vices inseparable from habitual indolence are engendered. It is in the temperate regions, where nature is not lavish, but liberal, and yet requires the hand of labour and the head of thought, that the human race is presented to us in its highest form, whether bodily or mentally considered. It is in such regions that arts attain to perfection; that science walks hand in hand with religion. A thousand necessities urge to exertion and enterprise, and these are followed by a due reward.
Thus, then, are organic bodies, plants, the lower animals, and man, affected by atmospheric temperature; but man has called in heat, artificially produced, if we may use the word in a certain sense, to his aid. Without heat, ore could not be smelted, or instruments of metal made; glass and earthenware could not be manufactured; houses could neither be built, nor furnished with articles of utility; the operations of agriculture could not be successively carried on, nor ships built, nor steam engines or machinery be constructed, nor could man clothe himself or cook his food. In short, were it to please the Almighty to suspend the laws of caloric, man would be rendered at once helpless, and his senses useless; he must necessarily become a completely altered being, granting even that his continuance as a species upon the face of the earth were guaranteed.