国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ

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 Chu-
Nago coming from the north. Then the Chachu Sangpo, coming from N.N.E.;
there was a ferry-boat where the tasam 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 redis-
covered 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 Long tso.