Tables have been prepared of the average temperature at the Ben Nevis and Fort-William Observatories on each day of the year, using the records of the twenty years 1884 to 1903 inclusive. Table I. gives the average daily temperature at Ben Nevis, Table II. that at Fort-William, and Table III. the differences between them. These tables have been prepared as follows :—

Ben Nevis Observatory.—In summer the dry- and wet-bulb thermometers were exposed in an ordinary Stevenson screen 4 feet above ground, and in winter in a smaller-sized double-louvred screen, placed on a ladder-like stand, and moved up or down so as to be always about 4 feet above the surface of the snow. These thermometers were read hourly, and the average of the dry-bulb readings for the 24 hours of each day is taken as the temperature of that day. Table I. is the arithmetical mean of the values so computed on each day of the year.