Therefore, he says, the Brahmaputra below Ki-chu must at least be equal to the Indus at Attock. Here he makes a mistake. The country through which the upper Indus flows cannot be said to be like the country of the Tsangpo. It gets less precipitation and is generally drier. The mountains are lower. The distance to the Himalayan foot hills is shorter. Therefore more of the humidity of the ocean is stopped before it reaches the mountains round the upper Indus. The upper Tsangpo therefore receives more water and its tributaries are much greater than those of the upper Indus. But none of them, not even Raga-tsangpo, can be compared with the Shayok. For further west the precipitation again gets much more abundant. I should think that the Shayok, in summer, is several times bigger than the Raga-tsangpo. Montgomerie goes so far as to make each of the Tsangpo's six tributaries larger than the Ganges at Hardwar, and thus he gets for the whole river, below Ki-chu, a volume of 35,000 cubic feet per second, during the dry season, December and January. As Montgomerie calculates an average of some 5,000 cubic feet for every tributary, he gets 20,000 cubic feet for the Tsangpo just below the junction with the Chaktak-tsangpo, — during the dry season. How very vague and uncertain such calculations are may be seen by the fact, that at this very place the river, after having received the Chaktak-tsangpo, carried only 3,196 cubic feet on 29th of May 1907.
On the admirable and historically important map compiled by Montgomerie from Nain Sing's report, all the six large tributaries and several small ones are entered so far as Nain Sing could make out their course. We have first the ChuNago coming from the north. Then the Chachu Sangpo, coming from N.N.E. ; there was a ferry-boat where the tasanz crosses it. The real name of the river is Tsa-chu-tsangpo. The river of Nyuku he calls Minchu Sangpo; I heard it as Men-chu. Then follows the Charta Sangpo from N.N.E., receiving the Chaka Chu. The latter name probably comes from Saka, a place situated on this river. Nain Sing's Charta is the same as my Chaktak; if the name is quickly pronounced it may easily be misheard. The Shorta Sangpo is also entered on Ryder's map, where its lowest part crosses the Shote Tang. Raka Sangpo (Raga-tsangpo) is by far the best mapped of all the tributaries, as the route of the Pundit followed almost the whole course of this river. Both the Raga-tsangpo and its surroundings had indeed to be rediscovered by a trained surveyor, for here the Ta-ch'ing map was very wrong, and d'Anville's map still worse. And here Nain Sing really improved the Chinese map, which, as we have seen, cannot be said of his survey near the source. Only in one detail is his map of the Raga-tsangpo inferior to the Chinese, for he has not a single northern tributary, whereas the Chinese map, correctly, has three. Nain Sing also mapped in the two small lakes Nabring Kimcho and Lang Cho Gonak, both of which were on the Ta-ch'ing map more than a hundred years earlier, the first called Ghiit ghia mtso with, at its southern shore, a place called Djang abring (Dsong-nabring ? ), -- and Lon tso.
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