Oct. 1849. METEOROLOGICAL OBSERVATIONS AT 18,500 FEET. 175 



broke my azimuth compass. They left us to ourselves 

 when the fire I made to boil the thermometers went out, 

 the wind being intensely cold. I bad given my barometer 

 to one of Campbell's men to carry, who not coming up, the 

 latter kindly went to search for him, and found him on the 

 ground quite knocked up and stupified by the cold, and 

 there, if left alone, he would have lain till overtaken by 

 death. 



The barometer on the summit of Bhomtso stood at 

 15 '548 inches;* the temperature between 11*30 a.m. and 

 2'30 p.m. fluctuated between 44° and 56°: this was very 

 high for so great an elevation, and no doubt due to the 

 power of the sun on the sterile soil, and consequent 

 radiated heat. The tension of vapour was '0763, and the 

 dew-point was 5° 8, or 43° 5 below the temperature of the 

 air. Such extraordinary dryness f and consequent evapo- 

 ration, increased by the violent wind, sufficiently accounts 

 for the height of the snow line ; in further evidence of 

 which, I may add that a piece of ice or snow laid on the 

 ground here, does not melt, but disappears by evaporation. 



The difference between the dry cold air of this elevation 

 and that of the heated plains of India, is very great. 

 During the driest winds of the Terai, in spring, the tempe- 

 rature is 80° to 90°, the tension of vapour is "400 to "500, 

 with a dew-point 22° below the temperature, and upwards 

 of six grains of vapour are suspended in the cubic foot of 

 air ; a thick haze obscures the heavens, and clouds of dust 

 rise high in the air; here on the other hand (probably 



* The elevation of Bhomtso, worked by Bessel's tables, and using corrected 

 observations of the Calcutta barometer for the lower station, is 18,590 feet. The 

 corresponding dew-point 4° 4 (49° 6 below that of the air at the time of observa- 

 tion). By Oltmann's tables the elevation is 18,540 feet. The elevation by 

 boiling water is 18,305. 



+ The weight of vapour in a cubic foot of air was no more than jSgg of a grain, 

 and the saturation-point *208. 



