Abstract
A NEW method of comparing the brightness of different coloured lights has been proposed by Herr Briicke (Wien. Ber., 84). He finds that objects cease to be visible at a greater visual angle, the more they differ from the background on which they are seen, only in colour and not in brightness. If a board be set up, which is black at one end and white at the other, with successive shades of grey between (a brightness-table), one may determine the brightness, e.g. of a coloured paper, by placing a piece of it before different parts of the board, and noting the place where, with shortest interval, it becomes invisible. This relation of brightness, in red and blue, varies much with the strength of illumination, so that each determination becomes invalid, where the illumination is considerably altered. Herr Briicke believes such a table might be useful in the colourless reproduction of paintings (drawings, copper-plate engravings, &c.). Further, he constructs a photometer, in which, instead of the brightness-table, he employs a variable illumination of the object to be distinguished from it.
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Physical Notes . Nature 26, 138–139 (1882). https://doi.org/10.1038/026138a0
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DOI: https://doi.org/10.1038/026138a0