VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 545 



Road to Sanha, Sept. 12. The road still ascending to Sanha, and near the 

 river for 10 miles. The thermometer falling some degrees, we found it cold and 

 chilly. The bed of the river is full of large stones, probably washed down from 

 the mountains by the rapidity of its stream; they are chiefly quartz and granite. 

 Here is excellent pasture for numerous herds of goats. 



Road to Chichakumboo. From Sanha the ascent is much greater, and, after 

 keeping for 10 miles along the banks of the Pachu, still a considerable stream, 

 we reach its source, from 3 distinct rivulets, all in view, ramified and supplied 

 by numerous springs, and soon after arrive at the most elevated part of our road. 

 Here we quit the boundary of Boutan, and enter the territory of Thibet, where 

 nature has drawn the line stiU more strongly, and affords perhaps the most ex- 

 traordinary contrast that takes place on the face of the earth. From this emi- 

 nence are to be seen the mountains of Boutan, covered with trees, shrubs, and 

 verdure to their tops, and on the south side of this mountain to within a few feet 

 of the ground on which we tread. On the north side the eye takes in an exten- 

 sive range of hills and plains, but not a tree, shrub, or scarcely a tuft of grass 

 to be seen. Thus, in the course of less than a mile, we bid adieu to a most 

 fertile soil, covered with perpetual verdure, and enter a country where the soil 

 and climate seem inimical to the production of every vegetable. The change in 

 the temperature of the air is equally obvious and rapid. The thermometer in 

 the forenoon 34°, with frost and snow in the night-time. Our present observa- 

 tions on the cause of this change confirmed us in a former opinion, and incon- 

 testably prove, that we are to look for that difference of climate from the situa- 

 tion of the ground as more or less above the general level of the earth. In at- 

 tending to this cause of heat or cold, we must not allow ourselves to be deceived 

 by a comparison with that which is immediately in view. We ought to take in 

 a greater range of country, and where the road is near the banks of a river, we 

 cannot well err in forming a judgment of the inclination of the ground. Punukha 

 and Wandepore, both to the northward of Tassesudon, are quite in a Bengal 

 climate. The thermometer at the first of these places, in the months of July 

 and January, was within 2° of what it had been at Rungpore for the same periods. 

 They seem in more exposed situations than Tassesudon ; and, were we to draw 

 a comparison of their heights from the surrounding ground, I should say they 

 were above its level. The road however proves the reverse. From Punukha to 

 Tassesudon we had a continued and steep ascent for 6^ hours, with a very incon- 

 siderable descent on the Tassesudon side. From the south side of the mountain 

 dividing Boutan from Thibet the springs and rivulets are tumbling down in cas- 

 cades and torrents, and have been traced by us near to the foot of the hills, 

 where they empty themselves to the eastward of Buxaduar. On the north side 

 they glide smoothly along, and by passing to the northward as far as Tishoo- 



VOL. XVI. 4 A 



