Page:Popular Science Monthly Volume 79.djvu/37
CONCEALING COLORATION 33
Our book 6 was written only after all its facts were verified. It con- tains essentially nothing hut facts, and might have been called an expert's presentation of examples of consummate resemblances between animals' costumes and certain of their backgrounds. It has greatly surprised us that so many people have so slightly noticed the facts revealed as to take them for illustrations of a supposed " theory." The facts, themselves, are what we present.
From now on I shall be delighted to show to all comers to Monad- nock the perfect background-counterfeiting powers of all sorts of gorgeous birds and butterflies. I have already prepared good fac- similes of a zebra and the head of an oryx, to show the truly wonderful way in which when looked at from a creeping lion's or leopard's eye-level these animals pass for mere sky-vistas through the reeds or branches. My Washington deer was merely a crude beginning of the exhibitions that I can already give of this type of concealing-costume.
Any child who has access to a wide, open field away from lights can prove for himself that white does not show against a starlit night sky. And it is only fair to point out that any one so ignorant of the simplest laws of optics as to share the popular notion that it does, is not compe- tent to testify in this matter. Let the experimenter hold up between his eye and a clear, moonless night sky, a white card so inclined as to permit him to see its upper side. 7 Even in a wide, open field he can at most make it come as bright as the sky beyond it, and consequently vanish; but it can not of course get brighter than the sky. How could it, since it owes all its light to this very sky ! Yet Eoosevelt says : " At night, in the darkness, . . . the white rump-mark of the antelope is almost always the first thing about them that is seen, . . . and at night it does not fade into the sky, even if the animal is on the sky-line."
Many persons who hear of the vanishing-power I show in the brilliant bird-skins and butterflies and these white-topped animals sug- gest that in the animals' homes all might be different. I need only answer that when they see the vast range and astounding precision of what I show, this fear will vanish. The evidence is literally over- whelming. It is in every case only against a background notably like that of the animal's home that he will vanish.
6 ' ' Concealing Coloration in the Animal Kingdom. ' '
7 Moonlight, of course, or the uneven illumination from a cloudy sky, can make white show momentarily brighter than the sky; but nature has to deal in averages, and these very irregularities of illumination cause the prongbuck's white just as often to look too dark as too light.
Contradicting what he says of the skunk's white, Colonel Eoosevelt says: "After nightfall the zebra's stripes would be entirely invisible." Here again he is completely wrong, as if he had never hunted by night. These stripes are invisible at night until the enemy is near enough to endanger the zebra. Looked at as near as this, all colors except white, show strongly against a starlit sky.
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