Page:Popular Science Monthly Volume 24.djvu/833

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But this doctrine has its moral aspect also. The question of duty comes in at once and very obviously so soon as the actual consequences of conduct have been shown to be good or bad. But it may be well to show more definitely what the true line of duty is in regard to self. I shall, therefore, next consider cases where self-abnegation leads directly to the diminution of general happiness.—Knowledge.


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WHY THE EYES OF ANIMALS SHINE IN THE DARK.

By SWAN M. BURNETT, M.D.

THAT the eyes of some animals, particularly the cat, are luminous when they are in the dark, is a fact established from time immemorial. It is surprising, however, to find the exact nature of the phenomenon entirely misunderstood even by scientists whose lines of investigation lie in the particular field to which it belongs. In conversing, not long ago, for instance, with one of the first physicists of this country, who is at the same time an ardent sportsman, he gave me a graphic description of a "still hunt" for deer. This method of hunting, as is well known, consists in placing a bright light in the bow of a boat and propelling it noiselessly through the water. The deer is attracted by the light and goes toward it, but is prevented by its glare from seeing his enemies who are concealed in the shadow. The hunter, looking straight ahead, sees in the outer darkness—rendered Egyptian by contrast with the bright light immediately in front of his own eyes—two large, luminous bodies, like balls of fire. These are the eyes of his victim; and, making his calculation as to the distance from the eyes down to the breast, the valiant sportsman (who probably is also a strong anti-vivisectionist) fires, intending to send his bullet through the heart. The eminent physicist, in speaking of this luminosity, referred to it as due to the phosphorescence of the eyes, in that final way in which we are accustomed to speak of things beyond dispute.

But it is hardly less surprising to read in the article "Light," in the ninth edition of the "Encyclopædia Britannica," the following remarkable statement by Professor P. G. Tait, on the sources of light: "3. A third source [of light] is physiological; fire-flies, glow-worms, medusæ, dead fish (?)—the eye of a cat" (vol. xiv, p. 379).

If these are the opinions of acknowledged authorities in optics, we can hardly expect the mass of even ordinarily intelligent and informed persons to have more correct ones, and should expect thorough credence to be given to the story of the man who claimed that he was able to recognize an antagonist who struck him in the dark by means of the light emitted from his own eye as the result of the blow.