Abstract
HERE is another proof that violet is the third primary. Prof. Tyndall, with that sagacity which results from the right use of his imagination, has given us a reason for the blue colour of the sky. It is probably the true reason, and it proves that blue is not a primary colour. The smallest light-waves are those of the extreme violet. These, therefore, are the waves which will be reflected in greatest proportion by the minute particles of foreign matter in the air. Why is not the sky violet then, instead of blue? Plainly, because although violet predominates in the reflected light, there is also a small proportion of green and a still smaller proportion of red. Suppose the ratios to be 1 red, 3 green, 6 violet, and suppose the ratios for white light to be 1 red, 2 green, 4 violet. Then, the light of the sky will be white plus 1 green, 2 violet, which is blue. In Professor Tyndall's experiment on the decomposition of sulphurous acid gas by a beam from the electric lamp, he tells us that, as the particles of the sulphur cloud grow larger, the colour changes from pale blue to deeper blue, and then to whitish blue and white.
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MOTT, F. The Primary Colours. Nature 3, 307 (1871). https://doi.org/10.1038/003307c0
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DOI: https://doi.org/10.1038/003307c0
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