During almost every winter anti-cyclone, with its accompanying cold but calm and fair weather, the temperature at Fort-William is, for part of the time, nearly as low or lower than that on Ben Nevis, 4400 feet above it. The average difference of temperature is 16° Fahr.; Ben Nevis being that much colder, or about 1° for every 270 feet. But in anti-cyclones this normal difference of temperature is widely departed from, the records showing that Ben Nevis has been 17° warmer instead of 16° colder than Fort-William, a departure of 33° from the normal; and it has frequently been 5° to 10° warmer for a day or two at a time. These data only give the temperatures on the summit of Ben Nevis, and at the sea-level five miles away they give us no information as to what it is in the intermediate air. That there is something unusual in this 4400 feet of atmosphere is hinted at by two facts,—first, with this abnormal temperature arrangement we always have very dry air on the summit, and very damp air at Fort-William; second, the difference of the barometer readings at top and bottom is less than the normal difference for the temperature. The former is an inversion of the ordinary humidity conditions—usually the air on the summit is saturated, or nearly so, with moisture, and at Fort-William dry; the latter, the barometric differences, require a few words of explanation to show what exactly they indicate, and how they bear on the question of temperature.