Page:Popular Science Monthly Volume 4.djvu/599

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more rapidly than that for blue or violet. In fact, as I said some time ago, the violet nerves always lag behind. From this it happens that, if we place side by side a quantity of blue and red light, arranging matters meanwhile so that they appear to the eye to be of equal brightness, then, upon adding considerably but equally to their actual luminosity, it will turn out that the red light will quite outstrip in apparent brilliancy its rival. We have now two such squares of red and blue, side by side on the screen, and it is difficult to say which is the brighter; but, when I greatly increase their illumination, it becomes evident that the blue one has been beaten; or, better still, when I reverse the experiment, starting with red and blue squares, of equal and considerable brilliancy, then, upon turning down the light of the lan-tern, and rendering them both dark, the blue square remains visible after its red companion has vanished. As another example, I may mention the blue color of the sky, which still continues plainly perceptible at night, when the illumination is so feeble that other colors have disappeared. Dove has pointed out that, in picture-galleries, as the light of day fades out, the blue colors in draperies and skies retain their power longer than the reds and yellows.


It is owing to this circumstance that, in actual landscapes, seen under the comparatively feeble light of the moon, there is a prevailing tendency to blueness. This also explains the circumstance that a landscape, illuminated by bright white clouds, appears more yellow in general hue than when the clouds are not bright, though still retain-in their whiteness, the strong white light stimulating more powerfully the sets of nerves concerned in the production of yellow. I think we all know that, on dark, dull days, there seems to be a tendency to blueness in the coloring, even though we may not have paid much attention to the reverse phenomenon. All this is prettily illustrated by a very simple experiment of Helmholtz's, who noticed that the impression of a bright day was produced by merely holding a pale-yellow glass before his eyes, the tint of the glass being so faint as hardly to disturb the natural colors of the objects; the use of a very pale-blue glass seemed, on the other hand, to darken up the landscape, as though a cloud were passing over the scene.



I TAKE it for granted that most Americans who have traveled in England know of, if they don't actually know, Clapham Junction. It is a marvelous place is that Clapham Junction—a half-dozen or more naked-looking graveled platforms, destitute of almost every con-