MANY descriptions of the green flash have been published in letters to NATURE and elsewhere, but I do not remember to have seen a satisfactory explanation of this curious phenomenon. Atmospheric dispersion is invoked, but this does not explain the absence of the red end of the spectrum. My observations agree in every particular with those described by Mr. Whitmell in NATURE of March 11, p. 35. At sea I have observed a violet or blue tint occasionally, and on one occasion a red flash as the lower limb of the sun emerged from a cloud into a clear space very near the horizon.