XVI.—The Sun as a Fog Producer

Abstract

I Fear that most, on reading the above title, will think it is either a printer's or an author's error, and that the title ought to have been “The Sun as a Fog Disperser.” We are familiar with the sun's power of clearing away fogs; we so often see fogs clear away as the sun rises, that we seem to have shut our eyes to another side of the question, which is, that under certain conditions the very opposite of this happens, the air thickening and fogging as the sun rises. Some years ago it was noticed at Falkirk, especially during the winter months, that on many mornings on which the air was clear before sunrise it gradually thickened to a dense haze, or to a dense fog, while in pure country air the observer never noticed similar changes. The question naturally suggested itself, what was the cause of this difference between the air at Falkirk and that of the country? A series of meteorological observations was therefore begun to ascertain whether this occasional fogging after sunrise was merely an accident, or if it had any connection with the sun; that is, to ascertain whether its appearance was what we call fortuitous, or if it appeared according to any law in nature.