346 General Notes. [f^^ 



for mere illustrations of a theory. In every case, however, the picture 

 proves the optical fact, and also shows the reader how he may for himself 

 prove it out-of-doors, if he will carefully follow directions. 



Take, for instance, our Figs. 114-115, which show photographs of a 

 white card against a dark background and against the sky. In Fig. 115 

 the card is brightly conspicuous; in Fig. 114 it has vanished from its place, 

 merely because it was photographed from two feet loiver doim. Surely 

 naturalists mu.st realize that the visible card makes a certain impression 

 on the mind, while that in Fig. 114 makes no impression at all, unless 

 I call their attention to the fact that it is really there although invisible. 



I can prove to them in many ways that the case of an antelope's white 

 stern-patch is subject to the same laws. Men have always been of a stature 

 that made them, apt to see the deer's or antelope's lohite brightly defined against 

 the ground, — and whenever the animal displayed it from a higher ridge 

 so that it had the sky behind it, it was nearly or quite invisible to them, 

 and so made little or no impression on their minds. 



We will assume, however, that man's eyes, being normally five or six 

 feet above the plain, commonly perceive this white when it is displayed 

 within their field of vision. But coyotes', wolves', and cougars' eyes 

 are all below the level of this rear-patch, and just as commonly see it 

 against the shy as man sees it against the ground. Beyond all dispute 

 it is exactly the color not to show to the eyes of any of these predators. 

 Equally wrong-colored is it for the sight of the fawn (so often said to have 

 it for a guide), as well as for the adults when their heads are down in the 

 act of grazing. How can naturalists believe that nature would give this 

 'signal' a color that failed to succor the most helpless members of the 

 wearer's race, the young? // any naturalist will 07ice look at svch white 

 from the fawn's level in the night,^ he will see the absurdity of the old concep- 

 tion. 



We all agree that whenever the antelope flashes this mark it is a sign 

 of alarm. If it is, it must serve as a warning to all antelopes that see it, 

 exactly as naturalists now believe. It must put all the antelopes that 

 see it on the alert. There are, however, a number of other forms of sig- 

 nalling that obviously outrank it in .serviceability. This white rear is, 

 even when seen against the ground, only visible from one direction. The 

 upraised head of an antelope watchful and sniffing stands almost as high 

 again, and against the sky always shows dark, while its gesture always 

 betrays to kindred animals its emotion. So must the characteristic 



1 The experimenter will find that even out in the open field it is only when the 

 white surface faces more or less upward that it gets enough illumination to be as 

 bright as the sky and becomes indistinguishable. Whenever the sky is partly hidden 

 by trees the white gets too little light to match it. But while it often fails to be 

 bright enough to disappear, practically never anywhere in the night is it too bright. 

 It is at the moment when the white rear of the antelope, deer, or hare faces most 

 upward, at the highest part of his leap, and when his head is descending, that the 

 best 'obliteration' comes. 



