Page:Popular Science Monthly Volume 23.djvu/589

Rh Some Peculiarities of Color-Blindness.—Mr. R. Brudenel Carter defines colorblindness, in his Cantor Lectures on that subject, as incapacity on the part of the nerves of vision to respond to the stimulus which one of the three kinds of light is calculated to produce. It will help us to realize the nature of the defect to assume, which is not quite the case, that white light is composed of red, green, and violet in equal proportions and of equal luminosity; then to eyes which are incapable of seeing one of the colors, one third of the illumination of natural objects is extinguished, and the appearance the objects present is not that of their real color, but only of that fraction of their real color in which the two visible colors are combined in them. White is not white to the color-blind, but a mixture of green and violet to the red-blind, of red and violet to the green-blind, and so through the other shades and the other varieties of colorblindness. It is impossible to obtain an exact idea of what the color-blind see, except a person be examined who has one eye normal-sighted while the other eye is defective. Professor Holmgren has examined two such persons, one of whom was red-blind, the other violet-blind in one eye, with results tending to confirm what had been predicted on the subject in accordance with the Young-Helmholtz theory. The mistakes made by the color-blind in daily life are much less numerous and less remarkable than might have been supposed; so much so, that the recently acquired knowledge of the great prevalence of the condition has come as a great surprise to most of the world; and persons may live for years having the defect without knowing it till the fact is revealed by some unexpected test being applied in an unusual manner. The color-blind are seldom fully insensible to differences in the colors between which they can not distinguish critically. They learn by habit to perceive differences in the appearance of objects which are called by different color-names—difference it may be in shade, or in intensity of light—which they learn to associate with the color-names, and will so escape being caught. Men on railroads may thus learn to distinguish red from green lights by one of them being bright and the other dim, and may go for a long time without being found out. Their defect, however, will some day expose them, probably when they are least suspicious of its influence. It has been remarked that color-blind men regularly eliminate themselves from railway-service in the course of a few years, by a kind of unintelligent selection, so that they are never found among the old servants of any company. They get discharged for carelessness, or for drunkenness, for accidents which were really owing to color-blindness. It is evident from these considerations that no test of the color-sense can be wholly satisfactory that depends on calling the colors by their right names, for that becomes a matter of habit—not one that depends on the exhibition of differently colored lights, for the blindest know a difference, although not the difference, between them. Holmgren's variously colored worsteds, of about a hundred and fifty shades, which candidates are required to assort and match, afford the most satisfactory and a nearly perfect test.

Cat-Lore.—The origin of domestic cats is obscure, but seems by all accounts to fall somewhere within historic times. All the histories of ancient nations seem to go back to a time when they had no cats. M. Lenormant says that a wild cat was hunted and eaten by the Swiss lake-dwellers in the age of stone; but Africa, south of Egypt, appears to have been the cradle of the cat as a domesticated animal. Pussy appears in the middle-empire Egyptian monuments in the character of a retriever seated in the boat of the wild-fowl hunter, a circumstance indicating that those people had a strain that did not have as unconquerable an aversion to the water as our cats; and there have been cats, even in modern times, that could bring themselves up to diving after fish. The cat, like everything else, whether agreeable or horrible, was raised to the odor of sanctity in Egypt and became the emblem of the goddess Pasht, the Egyptian Diana. M. Lenormant believes, however, that this worship was comparatively late, and finds no trace of the animal among the monuments of the ancient empire. Under the earlier dynasties, Pasht was a lioness-goddess, and not till the twelfth dynasty, and the conquests in