THE letter on this subject from Mr. Sidney Melmore, in NATURE of Jan. 3, leads me to describe an experience of my own which may be of some little interest. Recently I was accidentally struck in the right eye with a dog-whip, and I was conscious of a faint mistiness in front of that eye. But I was surprised to find on looking at an electric light, on the same evening, that it was surrounded by a set of diffraction halos, two orders being visible. Unlike the case described in Mr. Melmore's letter, the space round the electric light was white and only the red ring of the first order halo was visible, whereas all the colours of the second order could be seen. A very approximate measurement of the first red ring gave its angular diameter as 7°, in fair agreement with the value quoted in Mr. Melmore's letter. An examination of the eye in a mirror showed that it was bloodshot, but revealed no trace of any abnormality in the part of the cornea immediately in front of the pupil. The intensity of the halos decreased with time, and they disappeared completely after five days. It would be interesting to know the nature of the small particles responsible for the halos, and how they were produced by the blow.
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