Optical Phenomena in the Atmosphere


THE arc through the sun described by Mr. C. J. P. Cave1 can only, I fear, be identified with the horizontal circle and not with some rare tilted arc. Its identity is clear from the fact that it passed both through the sun and through the parhelia to the 22° halo, which have the same altitude as the sun. The impression of upward tilting, due to perspective, was unquestionably enhanced by the comparatively high sun and the small amount of the circle that was visible; a lower sun and a more extensive development of the circle make it clear that all parts of it are the same distance from the horizon. The apparent tilting is an effect with which Mr. Cave will certainly be familiar from observations of clouds.

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