Page:Popular Science Monthly Volume 29.djvu/836

816 as far as it is concerned would be much simplified; but I shall endeavor to show that black is not a negative impression. All black pigments and materials reflect light, and many of them to an extent which makes the fact readily demonstrable. Compare under a bright illumination half a dozen black things to be found in any home—cloths, book-covers, etc.—and it will be seen on a more or less close examination that they are not identical in appearance. Color-makers have their blacks of various intensities and shades. One of the commonest of blacks, lampblack, in comparison with some others, appears a very obvious gray. These black surfaces and pigments can not all be devoid of reflecting power, as they would then be incapable of making any impression upon the retina, and the differences must therefore be due to the various amounts or kinds of light which they reflect. Moreover, light reflected by black pigments is white light; that is, they reflect all the different kinds of rays in sunlight. Professor Rood ("Text-Book of Color") found that the black pigments used in his experiments reflected from two to six per cent as much white light as white paper (which, itself, reflects about forty per cent of the light falling upon it), the light being the same in kind and quantity as that from white paper under a sufficiently feeble illumination. There are, it is true, small differences in black pigments in power of reflecting the various components of white light. Blue may be slightly in excess of the normal proportion in white light, and so on, but these are so trifling that they do not affect the question before us. A black pigment with no reflecting power seems to be unknown, and is probably an impossibility. And it is by no means certain that absolute darkness should be taken as a standard of blackness, for several reasons. The impossibility of reaching the standard in practice and of making comparisons in perfect darkness would render it valueless. But the most important objection to it is this: after the retina has ceased to be affected by light, there become manifest certain subjective impressions, perhaps caused by circulation of the blood in the retina, which are not at all suggestive of black; in fact, a very black pigment appears to the writer much "blacker" than the darkness of a closet. The influence of contrast, which is of course impossible in perfect darkness, seems to be necessary to the impression of the most intense black. An utter absence of retinal excitement would, of course, be no sensation at all, and would be of no more use as a standard of blackness than is the blind spot of the eye, of which we