FLORA OF TIBET OR HIGH ASIA. 133 
is very dry, and the sun’s power in the rarefied and usually 
cloudless sky very great. The vegetation is meagre in the last 
degree; and in the tract that I visited, which, being much nearer 
to the Himalaya than the region through which Capt. Bower 
passed, is no doubt better supplied with moisture, I estimated 
that not one-twentieth part of the surface was covered with 
vegetation. The comparison of Mr. Thorold’s collection of 
plants with that made by Mr. E. Winterbottom and myself in 
1847 will be of considerable interest.” 
Messrs. Schlagintweit’s meteorological observations did not 
cover more than two or three seasons, and in many districts less ; 
but they afford some idea of the climate of Western Tibet and 
the adjoining countries. They calculated the annual mean 
temperature at 16,500 ft. as follows :— 
Outer Himalaya, southern slopes ............ 32° Fahr. 
Inner Himalaya, southern slopes ............ 29°5° 
Western Tibet, and northern slopes of the 
Himalaya and Karakorum chains ......... Ble, 
Kuen Luen, both sides of the crest ......... 20°5° ,, 
The mean decrease of temperature for altitude, the result of 
a great number of observations, was 1° Fahr. for 390 ft. The 
decrease of temperature in latitude is analogous to that in 
Central Europe, namely 2° Fahr. for 1° of latitude; but in High 
Asia, when the isothermal lines are reduced to the level of the 
sea, there is a decided decrease of temperature from west to east. 
The conditions of atmospheric moisture are exceedingly irregular 
over the different parts of High Asia. In Tibet the annual 
amount of rain varies between two and six inches only, whilst in 
Sikkim, in the eastern Himalaya, it exceeds 120 inches a year. 
This is of special importance with regard to the vegetation. The 
difference in the relative humidity of the atmosphere was found 
to be much greater in Tibet than previous data might have led 
us to expect. The dryness was frequently 80 great that only 
1 to 13 per cent. of relative humidity was obtained _ . 
In a comparatively recent summary of the rainfall of the 
earth, Supan gives the total amount of precipitation in the 
Pamirs, at Leh, and at Urga. The observations in the Pamirs 
were made at a Russian military post, near the confluence of the 
rivers Murghab and Ak Baital, in about 78° 6' and 38° 8’, at an 
altitude of a little over 12,000 ft., and extended over one year 
only. The total for the year was rather less than 19 inche 
