to southern seas are unable to say enough of the splendid colors conjured up by the coral reefs.
But even this is not all. All lakes and seas swarm with swimming or "pelagic" plants and animals. Green and yellow, one-celled, microscopic algæ are exceedingly common to a considerable depth; and green and yellow algæ sometimes come to the front in such masses that "the Red Sea" becomes no arbitrary designation, but the correct expression of an observed fact. I have seen the bay of Villafranca colored partly red by millions of swimming Anchinia rubra about as large as peas; I have seen mile-long strips, several metres broad, immediately along the shore on the Riviera, colored a deep royal blue by compressed masses of swimming salleemans (Velella spirans).
We can not absolve the transparent swimming water-organisms, from the larger medusa down to the infinitesimal microbes, from having a certain amount of influence on the color of water. We should not be able to see their crystal-clear bodies if they did not refract the rays of light in a different direction from the surrounding water. By this means they send out a multitude of refracted rays, which singly are of little importance, but in the aggregate must produce an effect through their accumulation when millions of these living beings are crowded into a cubic millimetre. To what purpose should we have in some parts of the retina of our eye a million of sensitive elements or rods to the square millimetre, if we could not seize single impressions and unite them into a view of the whole?
Finally, we will not forget the air that is mixed with the water. If we shake a viscous fluid in the air, it becomes whitish, and at last white, like milk. Yet the fluid and the air are both transparent. But the air-bubbles scattered through the water refract the light in another way. The wave looks whitish, quite white on its edges, from the inclosed air, and as the motion grows stronger the white becomes more prominent, with a greenish tone when the water is clear and the sky clouded, radiant yellow in sunshine, and clay-yellow when the water is not clear. All these tones mix with the colors of the deep, and with the mirror-colors of the surface. Thus the question of the causes of the colors of water rises to be one of the most complex problems of science as well as of art, the full solution of which has not yet been reached, in spite of the various efforts of men of science and of pictorial artists, because in order to meet the apprehension of the common eye they have to continue into a picture the endlessly changing colors and shapeless figures which the sea affords. But when I stand before a wave painted by Mazure in Paris (he is there usually called Mazure le Vague, the Wave-Mazure), and see how that artist, without help of shore, walls, buildings, or ships, which sup-
