3 o6 THE POPULAR SCIENCE MONTHLY. 



perceive the clilorific and chemic rays, that is to say, the ultra-red and 

 ultra-violet ones, which do not affect our retina ? Bert's experiments 

 enable us to answer that they do not. That physiologist is even led 

 to assert that, with regard to light and the different rays, all animals 

 experience the same impi*essions that man does. 



Let us now look at the influence of light upon the color of the skin 

 in animals, noticing first the being which presents the strangest pecu- 

 liarities in this respect, the chameleon. This animal, indeed, experi- 

 ences very frequent modifications of color in the course of the same 

 day. From Aristotle, who attributed these changes to a swelling of 

 the skin, and Theophrastus, who assigned fear as their cause, to Wal- 

 lisnieri, who supposes them to result from the movement of humors 

 toward the surface of the animal's body, the most different opinions 

 have been expressed on this subject. Milne-Edwards, thirty years 

 ago, explained them by the successive inequalities in the proportions 

 of the two substances, one yellowish and the other violet, which color 

 the skin of the reptile, inequalities due to the changes in volume of the 

 very flattened cells that contain these substances. Bruck, renewing 

 these researches, proves that the chameleon's colors follow from the 

 manifold dispersion of solar light in the colored cells, that is to say, 

 from the production of the same phenomenon remarked in soap-bubbles 

 and all very thin plates. Its colors, then, come from the play of sun- 

 light among the yellow and violet substances distributed very curiously 

 under its wrinkled skin. It passes from orange to yellow, from green 

 to blue, through a series of wavering and rainbow-like shades, deter- 

 mined by the state of the light's radiation. Darkness blanches it, 

 twilight gives it the most delicate marbled tints, the sun turns it dark. 

 A part of the skin bruised or rubbed remains black, without growing 

 white in the dark. Bruck satisfied himself, moreover, that temperature 

 does not affect these phenomena. 



All animals having fur or feathers are darker and more highly 

 colored on the back than on the belly, and their colors are more intense 

 in summer than in winter. Night-butterflies never have the vivid 

 tints of those that fly by day, and among the latter those of spring 

 have clearer, brighter shades than the autumn ones. The gold-and- 

 azure dust that adorns them harmonizes with the tones of colors in 

 surrounding Nature. Night-birds, in the same way, have dark plu- 

 mage, and the downiness of their coverings contrasts with the stiffness 

 of those that fly by day. Shells secluded under rocks wear pale 

 shades, compared with those that drink in the light. We have spoken 

 above of cave-animals. What a distinction between those of cold 

 regions and those of equatorial countries ! The coloring of birds, 

 mammals, and reptiles, peopling the vast forests or dwelling on the 

 banks of the great rivers in the torrid zone, is dazzling in its splendor. 

 At the north we find gray tints, dead and of little variety, usually close 

 -upon white, by reason of the almost constant reflection from snow. 



