I HAVE examined Mr. Benham's top by the light of a bright sodium flame, but have failed to see anything like the colours which I see by daylight or by the light of an incandescent electric lamp. By the sodium light the outmost three circles appear, when the rotation is one way, to be dark brown, the inmost three dark leaden grey, while the intermediate circles are paler brown. Reversing the direction of rotation interchanges the appearances of the outmost and inmost three circles. I cannot see any red or blue, or green, in any case. Other people here seem to see much the same as I do when the top is illuminated by the sodium flame only. With certain black and white figures of my own, I can get a pink appearance in the sodium light, but no green or blue. With spiral figures, which are worrying to look at, I find that some people can see a play of colour even with the sodium light, but I do not see it myself. Using a turn-table, by which the rate of rotation can be regulated at will, I have found that the speed, in white light, required to bring out the colours is decidedly different for different people. This fact convinced me that the explanation of these very curious appearances must be looked for in some physiological cause. It is perhaps worth remark that a sodium flame, when there is much sodium in it to make it bright, is by no means monochromatic, though sufficiently so to make the experiment with the top a very interesting one; and as Mr. Benham sees colours by this light which some others fail to see, it goes far to prove the phenomenon to be subjective.
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LIVEING, G. The Artificial Spectrum Top. Nature 51, 200 (1894). https://doi.org/10.1038/051200d0
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