may be permitted to consider here a few of the conditions that have an influence on the general effect.
A still-water surface forms a mirror which reflects those colors of the horizon that fall upon it at the same angle as that under which the eye stands to it. When I am at the shore of a quiet sea, or of a still lake, the water beams with the colors of the horizon. In a bay surrounded by woods, I see a deep gray; on the broad surface at sunset, the liveliest yellows and reds; looking straight down from my boat, the blue of the sky over my head.
These reflected colors concern the physicist the least, for he knows that every reflecting surface returns them; but they interest the painter almost exclusively. They constitute the tone of his landscape; they enliven the otherwise monotonous, dead surface, and he as well as the looker at his picture receives chiefly the impression of them. They are for the most part the colors of the lower horizon, for the point of view of the spectator is usually only a few metres above the level of the water.
Thus with the smooth mirror. But the scene changes immediately upon the slightest agitation. It is very seldom that the sea is quite still. The waves form hills and valleys, their surfaces are more or less inclined, and they reflect not the horizon with its down-toned colors, but the more saturated tints of the zenith. Whoever has seen the Mediterranean Sea or the Lake of Geneva under a cloudless sunset, and a slight rippling of the waves, will recollect that the surfaces glowing with burning yellows and reds, are broken up by sharp, deep-blue lines; they are the wave-valleys, which, by reason of their oblique inclination, turn the blue colors of the zenith into the eye. But this is not all. With the smooth mirror surface, and lower point of view, the eye not only receives the rays reflected from the surface, but it pierces through the inclined parts of the wave-valleys into the mass of the water, and thus perceives the proper color of the water, more intensely as the small surface of the wave-valley stands more perpendicularly to the eye. If the waves are very short, and follow one another rapidly, this impression of the color of the water will overcome that of the reflection. I can satisfy myself of this fact at any time.
The windows on the western front of my house look toward the Arve, which is here crossed by a dam that causes a fall of about a metre. Above the dam, the glacier-stream, colored a grayish yellow in summer and green in winter, is perfectly smooth; and from my windows, which are situated about six metres above the river, I can see hardly any but the mirror colors, yet a little mingled with the proper color of water, which appears considerably stronger when the sky is covered and its glaring light does not—as the painters are accustomed to say—"eat up"
