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Show A NOTATIONS AND ADDITIONS. 93 bushes which serve the inhabitants for fuel to warm their huts, attain, in the latitude of 30!0 and 31° of north latitude, a height of 2650 toises (16,945 English feet), or almost 200 toises (1279 English feet) higher than the limit of perpetual snow under the equator. From the data hitherto collected it would follow, that we may take the lower limit of perpetual snow on the northern side of the Himalaya, on the average, and in round numbers, at 2600 toises, or about 16,600 English feet; whilst on the southern declivity of the Himalaya the snow-line sinks to 2030 toises, or about 13,000 Engli h feet. But for this remarkable distribution of temperature in the upper strata of the atmosphere, the mountain plain of Western Thibet would be uninhabitable to the millions who dwell there. (Compare my Examination of the Limit of Perpetual Snow on the two declivities of the Himalaya, in the Asie Centrale, t. ii. pp. 435-437; t. iii. pp. 281-326, and in Cosmos, Engl. ed., vol. i., note 403; s. 483 of the original.) A letter which I have just received from India from Dr. Joseph Hooker, who is engaged in meteorological and geological researches, as well as those connected with the geography of plants, says: "Mr. Hodgson, whom we regard here as the geographer best acquainted with the hypsometric relations of the snow ranges, completely recognizes the correctness of your statement in the third part of the Asie Centrale, respecting the reason of the inequality in the height of the limit of perpetual snow on the northern and southern declivities of the Himalaya. In the 'trans Sutlej region' in 36° lat. we often saw the snow limit only commence at an altitude of 20,000 English feet, while in the passes south of the Brahmaptura, between Assam and Burnum, in 27° lat., where the most southern Asiatic snowy mountains are situated, the limit of perpetual snow sinks to 15,000 English feet. I believe we ought to distinguish between the extreme and the mean heights, but in both we sec manifested in the clearest manner the formerly contested differences between the Thibetian and the Indian declivities. |
