The Knickerbocker, Vol. 10, No. 6, December 1837

by Various

There can be no more interesting object of attention, than the examination of the evidences of design, as exhibited in parts of the intricate machinery of Nature. Physical principles, which, at first sight, or indeed after much philosophical investigation, have appeared of but limited importance, or perhaps wholly accidental or unnecessary, have, upon farther study, been found to rank among the number of most beautiful and convincing proofs of creative intelligence; have formed the most important links in the chain which holds together the material universe.

Such has been the train of thought suggested to the mind of the writer of this article, by an examination of the nature and physical relations of COLOR. This property of matter might appear to a superficial observer as one of inferior importance. He would admit that the differences of color add to the happiness of the human race, inasmuch as they give variety and beauty to material objects, and afford one of the most easy methods of distinguishing them from each other, but would probably deny that the existence of animal life is at all dependant upon color, and that it is essential to the present constitution of things. But let such an one reflect a little more upon this property—let him consider attentively all its relations—and he will doubtless change his opinion.

In travelling from the equator toward the poles, we cannot but be struck with the fact, that there exists a difference of color corresponding to a change of climate. Under the equator, the covering of the earth, that is, the vegetation, is darker than in any other part of the globe; and, as there is but little change of climate through the year, this dark covering does not give place either to the light tints of autumn, or to the snowy robe of winter. In advancing north, the foliage becomes lighter in proportion to the increase of latitude. In the temperate zone, the dark, rich robe of the tropics gives place to one of livelier hue, which, after covering the earth during a part of the year, assumes the light colors of decay, and is buried beneath the snow. Thus this change continues to keep pace with the diminution of temperature, till we enter the frigid zone, and reach the region of eternal frost.

From this difference of color in the north and south, and in summer and winter, we may deduce this general fact, that the earth adapts itself in color to the variations of temperature, presenting a dark surface to the heat of summer and the tropics, and a light one to the cold of winter and the frigid zone.

So much then for the fact. Let us now consider the design of such an arrangement. When a body contains more caloric than the air, or the other bodies by which it is surrounded, heat is given off from it in all directions, till the equilibrium is restored. Three, and perhaps more, physical operations take place in this case; radiation from the heated substance, reflection and absorption by the surrounding bodies. Now it has been proved, by repeated experiment, that these changes depend, as it regards their extent and rapidity, upon the color of the bodies. The more light-colored the heated substance is, the more slowly will it part with its superfluous caloric. Were it entirely black, the change would take place with more rapidity than in any other case. If the surrounding bodies were of a light color, a large portion of the heat radiated upon them would be reflected, and but little absorbed. Just the contrary would take place were they dark. The caloric would nearly all be absorbed, and but little reflected.

Similar to these are the phenomena of light. Bright substances reflect, and dark absorb, the rays from a luminous body. This, however, is hardly a correct method of expressing the fact intended. Philosophers believe that darkness of color is not the cause of the absorption of the luminous rays, but, on the contrary, that this absorption is the cause of the darkness. The fact in question then is this; some bodies are of such a chemical constitution, that they readily absorb light, and, as a consequence, little being reflected to the eye, they appear dark. Others, differently constituted, reflect nearly all the light that is thrown upon them, and, therefore, the lightness of their color bears proportion to such reflection.

Let us apply these facts to the explanation of the design of the geographical distinctions of color, of which we are treating. Suppose that the arrangement were different. Suppose, for instance, that the portion of the earth near the equator presented, throughout the year, a white surface to the sun. The rays of heat from that body would nearly all, upon reaching such a surface, be reflected back into the atmosphere, and would heat that part of it immediately bordering the earth, and most exposed to this reflection, to such a degree as to make the climate insupportable. The consequence would be, that a large portion of the earth would be rendered uninhabitable. But, by the existing provision, the rays of caloric pass directly through the air, heating it comparatively little, and are, for the most part, absorbed by the earth. The principle is similar in regard to light. Had the constitution of the covering of the earth in the tropics been such as to reflect the luminous rays, which are far more numerous and brilliant there than at the poles, the overpowering glare of light would alone have been sufficient to render those regions uninhabitable by any known species of animals.

Again: Let us suppose that the earth were clothed with a dark covering in the frigid zone. The few and oblique rays of heat, in that part of the globe would, after imparting but little of their caloric to the atmosphere, in their passage through it, be absorbed by the earth. The same effect would take place in regard to the rays of light, which are similarly few and feeble. It is easy to perceive the effect these things would have in darkening the polar regions, in greatly diminishing the temperature of the atmosphere, and, as a consequence, in contracting the extent of the inhabitable part of the globe. Thus we see, that by means of the snow, nay, by one, and as some would think, the least important of its properties, i. e., its color, man and his fellow animals are enabled to live in regions, the climate of which, without the instrumentality of this property, would destroy them.

After speaking of the change of color corresponding to change of latitude, it were superfluous to dwell at length upon the corresponding change of season, since the principle is precisely the same in each case. There can be no doubt but that in the temperate zone, the climate throughout the year is to a great extent equalized by this happy arrangement; that, without it, our winters would be much more rigorous, and our summers proportionably oppressive.

In passing, we might speak of another evil that would arise from snow being of a darker color. Upon a sudden change of temperature, it would melt very rapidly, and, if collected in any quantity, would occasion dreadful inundations, which would sweep and desolate the country. Such accidents occur even now in some parts of the world. How much more frequent and destructive they would be, in the case we have supposed, it is easy to conceive.