Who then can deny that we have, in the general principle which unites these phenomena, a well-attested instance of benevolent design? Who will assert that so beautiful and necessary a provision could be the result of chance?
But perhaps some one will say: 'It is true that there appears to be a happy adjustment of the color of the surface of the earth. It is true that this adjustment has an important influence in diminishing the difference of the temperatures of the polar and equatorial regions, and in rendering them both fit abodes of animals. But then, unhappily for the symmetry of the whole theory, no exception to the general principle is made in favor of the animals themselves. The inhabitants of the torrid zone, and man in a more marked and invariable manner than all the rest, are distinguished by the dark color peculiar to that part of the globe; so that they absorb the heat in an equal degree with, or perhaps greater than, the earth, since its color is even lighter than theirs. We find the same fact to exist as we advance from the equator toward the poles. The covering of the greater part of animals becomes lighter proportionally with the surface of the earth. In the frigid zone, the light color of man as well as of other animals, for instance the white bear, ermine, etc., must necessarily repel from their bodies by reflection a quantity of heat proportional to that which the atmosphere gains by reflection from the snow. This fact strikes us still more forcibly in the temperate zone, where the difference of climate, resulting from change of season, is greater than in any other part of the globe. Here our color is actually darkened by the heat of summer, in proportion to our exposure to it, and becomes lighter at the approach of winter. So that we are rendered by the heat itself more capable of absorbing it, and, consequently, of suffering from it. Surely, we cannot consider these things as evidences of design.'
But let us attentively examine these facts, and we shall find that the seeming difficulty disappears, and that the truths which gave rise to it, unite in a symmetrical whole with the others which we have mentioned, to form a cumulative and unanswerable argument in favor of the existence of a benevolent Creator.
Animal bodies do not depend for the quantity of caloric necessary to their existence upon the sun. By chemical changes, not yet well understood by philosophers, depending upon that subtle ethereal principle which we call life,[3] a sufficient quantity of animal or vital heat, as it is called, is evolved within the body itself. As this heat is constantly generated, it is necessary, in order that the body may not acquire too high a temperature, that it be as constantly conducted or radiated off. When the atmosphere contains too little caloric, its power of absorbing heat is so great as to deprive the animal body of it more rapidly than it is generated; thus producing the sensation of cold. On the contrary, when the weather is too warm, the air and other surrounding bodies, having less attraction for caloric, do not withdraw it as fast as it is generated; thus producing the feeling of heat. Perhaps, however, this is scarcely a scientific method of stating the fact in question. It is generally supposed by philosophers, that all bodies, whether in equilibrium, as it regards temperature, with surrounding substances, or not, are constantly radiating and absorbing caloric. When equally heated, the cause of their continuing so is, that they receive as much as they give off. When unequally heated, that which contains most caloric radiates more than the rest, and, of course, absorbs less than it parts with. By this means, an equilibrium of temperature is after a time brought about. Now, in cold weather, the heat which an animal body radiates is greater in quantity than the sum of what it generates itself, and absorbs from the sun and other bodies. The consequence is, it experiences the feeling of cold. In warm weather, the caloric radiated is less than that absorbed and generated; in which case, the animal suffers from heat. The vital heat of the generality of quadrupeds and other warm-blooded animals is several degrees greater in intensity than that of the atmosphere, during the warmest season in the tropics. The temperature of the human body is about ninety-eight degrees. The mean equatorial temperature Humboldt proved by repeated experiment to be eighty-one and a half degrees. It is evident, therefore, that in warm regions it is more important that the physical state and constitution of animal bodies should be adapted to the radiation of internal, than to the reflection of external heat, since the intensity of the former exceeds that of the latter.
Now we have before mentioned the fact, that the rapidity of the radiation of caloric from a heated body is in proportion to the darkness of its color. This then, taken in connection with the facts just stated, readily explains the reason why the color of animals varies with the temperature. The negroes of Africa, for example, are provided with a dark complexion, in order that the great quantity of heat which the warmth of their climate causes them to absorb, may be compensated for by an increased radiation. These unfortunate people, when they come to the north, as might be supposed, suffer at first extremely from the cold. They in time, however, become somewhat inured to it. Nature provides for them by another species of adaptation, which we cannot stop minutely to describe, but which may be proved to take place. The effect of it is to increase the evolution of animal heat, and thus to make up for the excessive radiation. Natives of high latitudes, however, are white, as has been said, and consequently their limited absorption of heat is compensated for by an equally limited radiation. We see, also, from this general principle, the design of the skin being so formed as to become tanned by exposure to the sun.
It is needless to dwell longer upon these facts. Taken in connection, they present perhaps one of the most interesting and harmonious arrangements that are to be met with in any of the departments of natural science. But it is by no means one of a few evidences of design, by which the advocate of religion may strengthen and confirm his faith. The whole universe is full of such examples. We have reason to believe, too, that we have but a very imperfect insight into the philosophy of Nature; that beyond the veil which separates the conquests of the human intellect from the vast tracts of knowledge, the possession of which yet remains to be acquired, there are myriads of beautifully-ordered systems, far surpassing in extent and grandeur any thing which the fancy of the wildest schemer has ever suggested to his mind. A few pebbles only have been gathered from the shore of the great ocean of truth. No wonder that the poet, impressed with this belief, should exclaim:
'There are more things in heaven and earth, Horatio,
Than are dreamed of in your philosophy.'
B. R. W.