Clouds and Shadows

Abstract

THE shadows to which Mr. Cyril Crossland refers in his letter to NATURE of May 30 have straight, fairly well-defined edges, and are therefore certainly cast by the sun itself, which would be still visible to anyone in the high reflecting layer, whether to east or west of the observer. They are certainly not cast by light “reflected from the glowing clouds in the west”, as Mr. Crossland thinks. The convergence of these rays towards the east, which the present writer has often seen, is purely a perspective effect. The rays themselves are in reality practically parallel, but seem to converge to east and west just as the parallel track of a straight railway seems to converge in both directions to anyone standing between the rails. The effect in the east soon after sunset is sometimes so striking that anyone might well believe that the sun had set there, were there no other circumstances to judge by.