Note 23 — Chapter XIII

The average degree of atmospheric transparency seems to be a most important element in determining the climate of any place. Dr. Richardson (Report to Brit. Assoc. for 1836, p. 131) has remarked that Professor Leslie, from experimenting on the effects of radiation only in an insular climate, deduced theoretical inferences respecting the mean temperature of the year, extremely different from the results obtained under the clear atmosphere of the polar regions. I apprehend central Chile will bear comparison with any part of the world for the clearness of its sky, and Chiloe, for one of an opposite condition: therefore we should not feel surprised, if the effects of two such opposite climates at first appear and malous. The remarkable difference in the height of the snow-line, on the opposite sides of the Himmalaya, has been explained by Humboldt and Jacquemont, on the same principle: and in a like manner, the difference between the heights on the Pyrenees and on Caucasus, the latter mountains being characterized by a climate more excessive, than that of the former.