90 Mr Hopkins on the Influence of Mountaim on Temperature, 



various ridges of mountains, the weather is in the autumn and early part 

 of winter very wet and warm for the latitudes. This is particularly seen 

 in Hindostan and the south-west coast of Italy ; while to the north-east 

 of these mountains the climate is cold and dry, extending over Poland, 

 Russia, Central Asia, and Siberia. The very heavy rains which fall to 

 the south of the Himalaya Mountains indicate the great condensation of 

 steam that takes place in that part of the world ; and the effect produced 

 on the climate is remarkable. The valleys are habitable to a great eleva- 

 tion, and Major Archer states, that wheat is grown at a height of 13,000 

 feet, in lat. 32'' north ; whilst Humboldt represents 1300 feet as the 

 greatest height at which wheat can be grown in TenerifFe, a place 4'' more 

 south. But when the steam that is in the atmosphere is all, or nearly 

 all, condensed against the sides of elevated ridges, it is evident that it 

 cannot carry its warming influence farther north. Hence the part of the 

 globe between these ridges and the polar regions will, in autumn and 

 winter, be dry and ver}' cold. In order to reason oh the causes of the 

 difference of winter climates in these latitudes, let it be supposed that the 

 present Asiatic mountains were removed further north — say to Northern 

 Siberia. Then, as there would be no longer elevated land to intercept 

 and condense the steam, where it is now condensed, it would flow far- 

 ther north, towards Siberia, and be there condensed, and it would render 

 that country, now so dry and cold in the winter, wet and warm. The 

 British Islands are now made warm in the autumn and the beginning of 

 winter by the steam that is brought from the tropical regions. But sup- 

 pose a lofty ridge of mountains to extend from the Canary Islands to New 

 York, and the effect would be, that the steam now brought north to more 

 than 50" of latitude, would be condensed 10° to 16° more south, and the 

 British Islands would be as cold in the winter as the same latitudes are 

 at present in Asia and America. That the relative situations of land and 

 water are not the cause of the great difference of climate, may be shewn 

 by supposing an alteration in certain parts of the earth's surface. Were 

 central Asia to become sea instead of land, that circumstance would not 

 prevent the present mountains from condensing the tropical steam, as they 

 now do, and consequently would not prevent that degree of cold and 

 dryness which results from the interception of that steam in those parts, 

 though they would be then sea instead of land. In like manner, suppose 

 a belt of low level land to extend from Spain across to Davis' Straits, 

 which is now sea ; and it will be perceived that this part, being land in- 

 stead of sea, would not, in the summer and autumn, prevent the tropical 

 steam from flowing to the British islands. It Avould not be until winter 

 had cooled down this supposed land below the temperature of the present 

 sea, that any greater condensation of tropical steam would take place 

 south of the British islands. From these various considerations, we are 

 warranted in coming to the conclusion that the great difl'erence in 

 the winter climates of certain parts of the northern hemisphere, is attri- 

 butable to elevations of land intercepting and condensing atmospheric 



