The phenomenon of silver thaw,—that is, rain falling when the temperature is below the freezing-point and congealing when it falls,—is of somewhat common occurrence at the Ben Nevis Observatory. A prolonged fall of silver thaw occasions considerable inconvenience to the observers; the rain freezes on their coats, gloves, and even on their faces, while everything outside becomes covered several inches thick with solid ice. But the most serious effect is the choking of the louvres of the Stevenson screen where the thermometers are, necessitating frequent changing of the screens.