Southern Tibet : vol.4 / Page 281 (Color Image)

0281	Southern Tibet : vol.4

with a boiling point thermometer and three aneroids, can never be sufficient to give
a correct absolute height. The atmospheric pressure changes constantly, and the
difference may be great from one day to another. The heights obtained are, there-
fore, only approximate, which, to a great extent, explains the discrepancies between
the altitudes given by different travellers for the same place. But as long as we
do not possess absolutely reliable means of determining the heights, we must be
satisfied with approximate values. When travelling along a river we have a means
of checking the altitudes given by the barometric instruments. Going down the
river every camp must be lower than the previous one. Therefore either the 4,652 m.
of Camp LXXXIII are too low, or the 4,664 m. of Camp LXXXV too high.
But Camp XCIII of 1901 which we found to coincide approximately with LXXXV
of 1906, was only 4,644 m., which certainly comes nearer the truth than the
4,664 m. of 1906. As to the fall of the river, it can only be fixed by levelling
with instruments of precision. The same is, of course, true regarding every undu-
lation of the ground. Like all other rivers, the Bogtsang-tsangpo has a very changing
current. At some stretches of its course the current is very slow, at others it even
forms small rapids. As in all rivers, the velocity of the current and the rate of fall
diminishes towards the mouth. The greatest fall is in the upper reaches of the
river. Such is also the case with the Bogtsang-tsangpo. On the 7.5 km. march
between Camps LXXXII and LXXXIII, the fall was as 1:136. But if we take
the whole distance from Camp LXXXII (or XCIV of 1901) down to Dagtse-
tso a distance of some 115 km. we get a slope of 1:661, which may indeed be
regarded as extremely gradual. This fact is also in accordance with the whole
structure of the country. The river is, as it were, searching for its way. The
small hills and ridges cropping up in detached and isolated groups, are the highest
parts of whole mountain ranges and systems which have in the course of ages been
buried to the greater part by the deposits of débris and detritus. On the surface
of these beds filling the intermediate spaces, and between the remains of mountains
still fighting against destruction, the Bogtsang-tsangpo is still, in its old age and
with constantly diminishing energy, working its way down to Dagtse-tso. At places
where it flows over nearly horizontal ground, as just below Camp LXXXV, it
describes the most fantastic bends and windings. Such is indeed also the case at
and just below Camp LXXXII, though here the slope is comparatively steep as
may be seen by the current; it even appears very distinctly on the photograph on
Pl. 17, Vol. IV of Scientific Results mentioned above.
On the night of December 9th, the temperature fell to —29.9°. By such cold
weather, most of the river was frozen solid. We continue down the valley to the
E. N. E. and finally N. E. with partly rocky, desolate and barren mountain ridges
of reddish, pink and yellow tints at both sides. To begin with, the ground is

National Institute of Informatics - Digital Silk Road Project
Digital Archive of Toyo Bunko Rare Books

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National Institute of Informatics - Digital Silk Road Project Digital Archive of Toyo Bunko Rare Books

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National Institute of Informatics - Digital Silk Road Project
Digital Archive of Toyo Bunko Rare Books