On Colour-Photometry and on Some Quantitative Relations of the Phenomenon of Purkinje (Classic Reprint)

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Excerpt from On Colour-Photometry and on Some Quantitative Relations of the Phenomenon of PurkinjeIt has sometimes been maintained that black can be seen better on a white background than white on a black back ground, and examples of printed letters are cited in proof. This is true only because we have shaped our letters in such a way that they are adapted for the use of black on white: the irradiation being different when white is the surface of the let ters rather than the background. Similarly Von has said that yellow on a blue background and green on red are more easily scen than blue on yellow and red on green, and he attributes this to the qualities of the colours. But if there is such a difference, it must be due to intensity rather than to colour quality. For if we place, for example, a black surface one inch square concentrically upon l white cardboard square of twenty inches to the side, we shall have 399 square inches of white and one square inch of black. Let us assume that the intensity of black to white is as t to so. Then we have the intensity of the whole surface equal to 399 x 50 plus i and if the whole surface had been white, we should haye had an inten sity of 4oo x so. So while the whole intensity would be zo, ooo, the existence or non-existence of the black square conditions a difference of intensity of 5 of the total intensity. The other hand, if the large surface is black, it has a total intensity of 400, and the white square will now cause an increase of 3097, to the total intensity.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.