Page:Popular Science Monthly Volume 27.djvu/708

688, it might be supposed that peoples who have continued in the conditions of the Stone age, like the natives of Cape Horn, should not have participated in the general progress. The French expedition, that recently spent a year at Terra del Fuego, made a special study of the natives in respect to this point. The Fuegian language has terms for only two colors, one for red and analogous tints, the other for blue and green. But it is thus poor only because colors do not play an important part in Fuegian life, for it was found that with a little practice the people learned to distinguish and classify colors and their different shades with all the exactness of the most civilized European. The organic development of their visual apparatus, therefore, leaves nothing to be desired. The question whether the vision of animals is the same as that of man, or whether some of them may not have the faculty of perceiving rays to which we are insensible, has been taken up by M. Paul Bert. He placed in a glass vessel a number of freshwater crustaceans of the family of Daphneæ. When light was cast upon a point in the vessel, the Daphnias precipitated themselves upon it and arranged themselves along the beam. Most animals show a similar disposition, and seek the light when it is not too glaring. When a spectrum was thrown upon the vessel, the Daphnias still spread themselves over the illuminated region, but with some quite remarkable peculiarities of arrangement. The smallest ones were scattered through the whole spectrum, being rare in the red, abundant in the yellow and green, and more numerous in the blue and violet, while some of them fixed themselves in the ultra-violet. The largest ones, however, were almost exclusively localized upon a narrow band situated between the green and the blue. These animals, then, see the same rays as we, notwithstanding the distance that separates them from us in the zoölogical scale, and even seem to share our infirmities, for some of them behaved as if they were affected by color-blindness. Sir John Lubbock has made a series of brilliant researches, in the laboratory of the Royal Institution, on the vision of ants, bees, and wasps, from which the curious result has been deduced that the ultra-violet rays appear brighter to ants than the ordinary luminous spectrum. The history of animals regarding this point would therefore be of the highest interest.

We have, so far, considered colors only as one of Nature's decorations, but their influence on the development of living beings is exercised under the most various conditions. Without doubt, light and colors act upon the condition of our mind, and the moral impression thus produced can be nothing but the translation of a physiological action. In some sanitary establishments, where mental disorders are treated, patients are sometimes kept in a yellow light, which seems to exercise a happy influence on their disposition, and to promote calmer feelings. It. is not the yellow light of soda that produces this result, but a kind of white light, in which the extreme blue and red rays have