EAST NEPAL AND THE SIKKIM HIMALAYA MOUNTAINS. 109 



Distribution of Temperature in the Three Zones. — A remark- 

 able uniformity prevails throughout the year at the lower zone, 

 there being, at 7000 feet, but 22° difference between the mean 

 temperatures of the hottest and coldest months ; whilst in Lon- 

 don, with a lower mean temperature, the equivalent difference is 

 27°. In the second (middle zone) at 11,000 feet this difference 

 is equal to that of London, In the upper it is still greater, the 

 climate becoming excessive at 15,000 feet, where the difference 

 amounts to 30° at least. 



Between 6000 and 10,000 feet, i. e. throughout the first zone, 

 I find the mean annual temperature decreasing with the elevation 

 at the rate of 1° to every 320 feet. 



Between 10,000 and 14,000 feet at 1° to every 350 feet. 



And between 14,000 and 18,000 feet at 1° to every 400 feet. 



This srives — 



15,000 feet being the limit of perpetual snow where that phe- 

 nomenon advances farther south in Sikkim, and 19,000 feet 

 the limit of perpetual snow in Tibet. Supposing the same law 

 to apply (wliich I exceedingly doubt) to heights above 19,000 

 feet, 2° would be the mean annual temperature of the summit 

 of Kinchinjunga, altitude 28,178 feet, the loftiest known spot 

 on the globe. 



The upper limit of plienogamic vegetation coincides with a 

 mean temperature of 30° on the south flank of Kinchinjunga, 

 and of 22° in Tibet ; in both cases animals and perennial-rooted 

 herbaceous plants are to be found at elevations corresponding 

 to these mean temperatures, and even at higher elevations in shel- 

 tered localities, I have assumed the decrease of temperature 

 for a corresponding amount of elevation to be gradually less in 

 ascending (1° =320 feet at 6000 to 10,000 feet, and 1° = 400 

 feet at 14,000 lo 18,000 feet). My observations appear to prove 

 this, but I do not regard them as conclusive ; supposing them to 



