Page:Popular Science Monthly Volume 79.djvu/33

Rh further off he is the more of this scrub actually comes between him and the spectator. There is therefore obviously some distance at which he is wholly covered by the scrub. Now from the very nose of the beholder all the way to the point where the animal is actually hidden by accumulated twiggery there is a scale of diminishing visibility, and, while the light favors the animal's background-matching, he becomes utterly indistinguishable from the scrub and grass long before he is at the point of actual eclipse. Yet Roosevelt is able to say: "There is never any difficulty in seeing them "! Compare Stewart Edward White's description of the evanescence of deer in similar situations, written before he ever heard of concealing-coloration.

It is when the light gets behind an animal that its main power to upset concealing coloration comes into play. Except in the middle of the day, there is always one direction which is toward the light, and looked at in this direction the sheltering ambiguities of these thin coverts have to give up many of their secrets. An hour earlier the antelope's imitation twig-haze passed all right, but now that the sun is low and streams through the whole gauzy growth, behold, the opaque antelope becomes a black silhouette on a light gray ground. He is not really a gauzy growth!

It is hardly worth while to say that all these laws of light and its relation to vegetation are practically identical the world over. Though I have been through most of Europe, from Norway and England to Italy and Sardinia, and through most of eastern North America, from Quebec to Florida, and in many of the Lesser Antilles and Trinidad (finding everywhere, what I knew before I went, that the laws of illumination of animals and vegetation are the same over the whole planet), I have not been in Africa. But—and this is more to the point—my critics have evidently not been in the land of the inexorable optics which govern this entire matter.

One of Roosevelt's most fundamental errors is his complete gap of perception about the effect of motion on concealing-coloration. In our book's introduction I say: "Thus at these crucial moments in the lives of animals, when they are on the verge of catching or being caught, sight is commonly the indispensable sense. It is for these moments that their coloration is best adapted, and, when looked at from the point of view of enemy or prey, as the case may be, proves to be obliterative." Had our critics studied this sentence, it would have saved them much misapprehension of what the book is about. But here let it suffice to remind them that the tennis-player's need of bright, clean, white balls, to be seen against the green turf, entirely refutes their ideas. The tennis-player calls for clean balls when the grass-stained ones are beginning to spoil his play; and well might a hawk, if his call would avail,