1865.] Notes on Central Asia. 129 



range. In the same zone, parallel with the Celestial mountains the 

 height of the snow-line is as follows : 



In the Pyrennees ; (between Lat. 42J° and 43° North), ... 8,400 ft. 

 On mounts Elburuz and Kazbek in the Caucasus (43° N. 



Lat.)... 10,170 ft. 



On mount Ararat (Lat. 39° North), 13,300 ft. 



In the Kocky mountains of N. America (Lat. 43° N.) 11,700 ft. 



Humboldt, in his observations on my letter to Eitter, refers exclusively 

 to the Pyrennees and to the Elburuz mountains. With regard to the 

 first they cannot be taken at all into account in determining the height 

 of the snow-line in the Celestial range, as they are situated in a moist 

 sea atmosphere, where the snow-line must be considerably lower than 

 in the continental climate of the interior of Asia. The Caucasus, 

 however, supplies a better point of comparison, if treated with proper 

 discrimination. The height of the snow-line of the Kazbek and 

 Elburuz occurs at 10,170 feet, under a latitude of more than 1|° to 

 the northward that that of the Tian-Shan, and with a climate consi- 

 derably more humid. On mount Ararat, where the surrounding 

 atmosphere is drier, and the latitude 2|° more to the south, we find 

 that the height of the snow-line is 13,300 feet above the level of the 

 sea. If a range of mountains existed between the Elburuz and mount 

 Ararat, under climatic conditions of an intermediate character as 

 compared to those characterising mounts Ararat and Elburuz, and 

 situated under the same parallel as the Celestial range, the height 

 of the snow-line of these mountains Avould be determinable at 11,300 

 feet. All these figures, computed theoretically by comparing the 

 heights of the snow-line on different parallels of the same meridian with 

 the Celestial mountains, and on different meridians of the same parallel, 

 coincide very nearly with my determinations. The considerable 

 elevation of the snow-line of the Celestial mountains is to be explained 

 by the peculiarity of their geographical position, and the character 

 of the surrounding atmosphere. It is generally admitted as a fact 

 that a dry atmosphere has the effect of elevating the line of eternal 

 snow very considerably. Thus for instance the snow-line on the 

 southern slope of the Himalayas occurs at 12,180 feet, while on the 

 northern side it rises to 15,600 feet. This anomaly is only to be 

 accounted for by the southern side of the range being exposed to winds 

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