Some twelve years ago I gave (Phil. Mag. March, 1867, “Climate and Time,” p. 548) what appears to me to be the true explanation of that apparently paradoxical fact observed by Mr. Glaisher, that the difference of reading between a thermometer exposed to direct sunshine and one shaded diminishes instead of increases as we ascend in the atmosphere. This led me to an important conclusion in regard to the influence of aqueous vapour on the melting-point ot snow; but recent objections to some of my views convince me that I have not given to that conclusion the prominence it deserves. I shall now state in a few words the conclusion to which I refer.