816 THE POPULAR SCIENCE MONTHLY, 



as far as it is concerned would be much simplified ; but I shall en- 

 deavor 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 com- 

 monest 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 quan- 

 tity as that from white paper under a sufficiently feeble illumination. 

 There are, it is true, small differences in black pigments in power of re- 

 flecting 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 prob- 

 ably an impossibility. And it is by no means certain that absolute 

 darkness should be taken as a standard of blackness, for several rea- 

 sons. 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 sub- 

 jective 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 dark- 

 ness of a closet. The influence of contrast, which is of course impos- 

 sible 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 



* With the writer these subjective images often take the form of a circular, or irregu- 

 lar, greenish ring closing in or contracting over a violet background near the center of 

 the apparent field of view, other similar rings succeeding each other in the same way at 

 pretty regular intervals. Although having no bearing upon the subject, it might be added 

 that these images, with others of a similar character, may always be observed in darkness 

 after retiring ; and I have a number of times thought I had detected, during the moments 

 between waking and dreaming, a merging of these images, with exaggerations and men- 

 tal accompaniments, into dreams. 



