Page:Popular Science Monthly Volume 2.djvu/321

Rh Not only the color of organized beings, but their shape too, is linked with the action of light, or rather of climate. The flora of the globe gain increasing perfection as we go from the poles toward the equator. The nearer these beings approach the highest degree of heat and light, the more lavishly are richness, splendor, and beauty, bestowed on them. The energy and glory of life, perfect forms as well as brilliant arraying, are the distinguishing mark of the various and manifold races in tropical regions, giving this privileged world its characteristic aspect. A pure emanation from the sun, Nature here lives wild and splendid, gazing unshrinkingly, like the Alpine eagle, on the eternal and sublime source which inundates it with heat and glow. Look, now, at the regions of the pole! A few dwarfish shrubs, a few stunted and herbaceous plants, compose all its flora. Its animals have a pale covering and downy feathers; its insects, sombre tints. All around them are the utmost limits of life—ice invades every thing, the sea alone still breeds a few acalephs, some zoophytes, and other low rudimentary organizations. The sun comes aslant and seldom. At the equator he darts his fires, and gives himself without stint to the happy Eden of his predilection.

It remains to note the relations of light to that being most sensitive to its influence, and best able to express its effects, man himself. The newborn child seeks the day by instinct, and turns to the side whence light comes, and, if this spontaneous movement of the infant's eyes is thwarted, strabismus may be the consequence.

Of all our organs the eye is the one that light especially affects. Through the eyes come all direct notions of the outer world, and all impressions of an æsthetic kind. Now, the excitability of the retina shows variations of every kind. Prisoners confined in dark cells have been known to acquire the power of seeing distinctly in them, while their eyes also become sensitive to the slightest changes in the intensity of light. In 1766 Lavoisier, in studying certain questions upon the lighting of Paris, which had been given for competition by the Academy of Sciences, found after several attempts that his sight wanted the necessary sensitiveness for observing the relative intensities of the different flames he wished to compare. He had a room hung with black, and shut himself up in it for six weeks in utter darkness. At the end of that time his sensitiveness of sight was such that he could distinguish the faintest differences. It is very dangerous, too, to pass suddenly from a dark place into a strong flood of light. The tyrant Dionysius had a building made with bright, whitewashed walls, and would order wretches, after long seclusion from light, to be suddenly brought into it. The contrast struck them blind. Xenophon relates that many Greek soldiers lost their sight from reflections off the snow in crossing the mountains of Armenia. All travellers who have visited