The barometer on the summit of Bhomtso stood at 15.548 inches;* [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 degrees (49.6 degrees below that of the air at the time of observation). By Oltmann's tables the elevation is 18,540 feet. The elevation by boiling water is 18,305.] the temperature between 11.30 a.m. and 2.30 p.m. fluctuated between 44 degrees and 56 degrees: 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 degrees, or 43.5 degrees below the temperature of the air. Such extraordinary dryness* [The weight of vapour in a cubic foot of air was no more than .087 of a grain, and the saturation-point .208.] and consequent evaporation, 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 temperature is 80 degrees to 90 degrees, the tension of vapour is .400 to .500, with a dew-point 22 degrees 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 owing to the rarity of the atmosphere and the low tension of its vapours), the drought is accompanied by perfect transparency, and the atmosphere is too attenuated to support the dust raised by the wind. We descended in the afternoon, and on our way up the Lachen valley examined a narrow gulley in a lofty red spur from Kinchinjhow, where black shales were _in situ,_ striking north-east, and dipping north-west 45 degrees. These shales were interposed between beds of yellow quartz conglomerate, upon the latter of which rested a talus of earthy rocks, angular fragments of which were strewed about opposite this spur, but were not seen elsewhere.