The average variability of temperature at any place is obtained by taking the difference of temperature at the same hour on successive days, and taking the mean value of this difference irrespective of sign. With a view to ascertaining whether this variability varied with the hour selected for comparison, the hourly temperature records at four places have been examined, and the day to day change of temperature at each hour noted. The places are—the Ben Nevis Observatory, the Fort-William Observatory, the Hong Kong Observatory, and the Arctic Station at Lady Franklin Bay, lat. 81° 44′ N., long. 64° 45′ W. At each place one year's record was taken, which, though too short a time to give a true mean, yet gives a fair approximation towards it. The mean values for each hour of the twelve months at the four stations are given in the accompanying tables, the highest value in each month being put in heavy type and the lowest in italic.