CH. Ill 



LOCALITY 



37 



In order to see at a glance how the temperature 

 decreases at different altitudes as compared with sea- 

 level, and taking 0*58 C. as the unit of decrease for 

 every 100 metres, 1 I append a statement showing this 

 for every 1000 metres up to 4000 : * 



This reduction of temperature according to altitude 

 has the tendency of changing the character of the 

 forests from tropical to subtropical, then to temperate 

 and sub-arctic, but it must be remembered that whereas, 

 in latitudes distant from the equator, the temperature 

 falls with the greater obliquity of the sun's rays and 

 the longer duration of nights during the winter, in the 

 mountains of the Tropics it is due solely to the rarefac- 

 tion of the atmosphere. This rarefaction has also other 

 effects. As the thinner air is not capable of retaining 

 more than a modicum of heat in its passage, it follows 

 that objects on the earth's surface take it up and thus 

 get heated more quickly, and, in the same way, part 

 with it also more rapidly. Everybody who has lived 

 at high elevations knows how quickly after sunset it 

 becomes intensely cold on a clear evening. A similar 

 difference will also be apparent between the temperature 

 in the sun and that in the shade. 2 In the mountains, 



1 For the convenience of readers not accustomed to the metric system and 

 centigrade thermometer, it may be stated that this works out at about 3 "17 

 Fahr. per 1000 ft. elevation. 



2 During an ascent of Monte Rosa made by the author in 1898, his party sat 

 in comfort on the southern side of the saddle, at about 14,000 feet, while a bolder 

 party of mountaineers tried to tackle the final peak while it was yet in shadow. 

 Owing to the intense cold and frostbite, however, they had soon to come back 

 to the saddle, and to wait for the sun before resuming their ascent. 



