Abstract
SINCE the appearance in NATURE of May 4 of the letter by Prof. Worley, with a brief comment by Lord Rayleigh, on this subject, further correspondence has been received confirming the suggestion that “the green flash is by no means a rare phenomenon”. Mr. H. Cary Gilson, Trinity College, Cambridge, states that he has observed the flash several times during the past five years from a point in Sussex 150 ft. above sea-level. In October 1933, while in the Gulf of Aden with the John Murray Expedition, “the flash could be clearly seen, with or without glasses, almost any evening”, and was even observed from a port-hole about 18 in. above the water. Mr. Northcote Thomas, Grove Cottage, West Malvern, Worcs, has sent a summary of observations made from the upper part of West Malvern, 800 ft. above sea-level. He states that a flash or similar phenomenon was seen on forty-one occasions between July 25, 1934, and April 20, 1935. The flash was green until about mid-September; blue or green from September 17 until October 8; blue from October 11 onwards. On occasions the colour persisted for half a minute. Previous volumes of NATURE will show that the green flash has already received considerable attention; and index entries to letters on the subject will be found in vols. 93-95, 110, 111, 120-123. The comparative frequency of the occurrence and the change of colour to blue were referred to, and also its appearance at sunrise as well as sunset. The weight of evidence, and particularly the sunrise effect, points to a physical explanation of the phenomenon, which is accepted by Prof. R. W. Wood in a letter in NATURE of March 31, 1928 (p. 501), where he suggests that the relative temperature of the atmosphere and the surface with which it is in contact is the determining factor; a cold surface with warm atmosphere would increase the normal gradient of refractive index, and also the curvature of the rays, so delaying 'sunset’ and affording “greater opportunity for atmospheric dispersion to come into play”.
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The Green Flash. Nature 135, 866 (1935). https://doi.org/10.1038/135866c0
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DOI: https://doi.org/10.1038/135866c0