Page:Popular Science Monthly Volume 41.djvu/262

250 the softer tones. But below the dam the water is in lively motion with endless little racing wavelets, and here the green color comes out so vividly that the reflection almost wholly vanishes. Yet another fact is revealed by the movement. Only with a perfectly smooth mirror surface are the outlines of the reflected objects fully clear and sharp. The reflection is then so perfect that one often hardly knows whether he sees the objects themselves or only their mirrored images on the water; and the lines between water and shore are quite effaced. The slightest movement causes the outline of the mirror picture to appear notched; clearer lines from the horizon creep into the darker colors of the picture, but notches from these, too, spring out over the lines which the outline should have. This phenomenon is so common that we notch the borders of water reflections in colored pictures, as well as in those drawn only in black. I have no doubt that a relationship lies at the bottom of this phenomenon like the fact observed by Colladon, and now often remarked, that water in motion carries the light along with it. A stream of water, flowing through a dark tube out of an illuminated receiver, carries the light along, whether it be white or colored, and shines; why should not moving waves exhibit the same effect?

But enough of these painters' impressions, which, as we have said, are neglected by the physicist, but are still of the highest significance for the beholder as well as for the artist, and, as may result from our representation, are dependent on various factors, among which, besides mirroring, the real color of the water is to be considered.

Let us go a little closer into this matter.

Pure or colorless water containing salts in solution is beautifully blue and perfectly transparent, at least to a certain depth. It is, hence, clear that with the color of all objects visible at this depth, and constantly reflecting the rays of light, is associated under the water a blue tone, more intensive as the depth at which the object lies is greater. The gravels on the shore of a lake or the sea become, when seen through the blue water, as if they were observed through a pane of blue glass; and since all shore figures, with trifling exceptions, are of a yellowish color, they will shine of a more or less green color, and the water on the shore will likewise appear green.

I here lay aside all physical deductions concerning the nature of color. We know that it is not, as was once thought, a property of bodies, but that a transparent body like water, for example, shows a distinct color, because it lets certain colored rays through, but not others, and that a solid body reflects the rays which we perceive, but to a certain extent absorbs the others. The discussion of the nature of color is not of very great importance for our essay.