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

¹It is beyond dispute that the Himalayan glaciers came down to a much lower level
in the past than they do to-day. Ancient moraines and evidences of glacial action
have been noticed at elevations varying from 5,000 feet to 8,000 feet by Hooker,
Macmahon, Godwin Austen, Blanford and others. The theory, once held, that the
Himalayas then stood at a greater elevation than is the case to-day, may be at once
dismissed, and we can safely admit that much lower temperatures prevailed in the
Himalayan region at that period. It does not, however, follow that the temperature
of the Indian peninsular area was appreciably lowered thereby.¹ ¹

The glaciers of Himalaya and Kara-korum begin in our days to attract more
and more attention. Some of the last visitors to the Kara-korum glaciers have been
able, by comparing their own maps with those of Godwin Austen and others, to
tell whether certain snouts have advanced or retreated. Such records will be more
reliable and numerous in future. And there will be a special study of the influence
of the monsoon rains upon the movements of the glaciers. We do not need to go
far back in time to become completely lost as regards information in these matters.
An augmented precipitation over the mountains will cause the snows to accumulate
and the glaciers to become more active and vice versa. But the glacier movement is
always delayed. The rise and fall of the levels of the Manasarovar and the Rakas-tal
would afford a much more delicate, reliable and convenient instrument for reading
the hydrographical influence of the precipitation. And if such records were carried
out for any considerable length of time, say 100 years, it would be possible to tell
in which direction the climatic changes proceed and with what speed, during the
present period. One should get the values of the periodicity, at least for the second
and third order; for the highest order a much longer time would be necessary.

But such regular records are, and will probably remain nothing but pious
desiderata, and at the present moment all we can do is to collect as much material
of observation as possible, and to try and draw out some general conclusions
from it.

The Tibetan plateau-land is very rich in lakes. As mean altitude for 37 lakes
in Western Tibet I found 4,837m., and for 58 lakes in Eastern Tibet 4,811m.,
so that the western lakes proved on an average to be 26m. higher. Comparing,
for instance, Deasy's six highest lakes in Western Tibet with my six highest lakes
in Eastern Tibet, I obtained means of 5,056m. and 5,001m., proving that Deasy's
lakes were on an average 55m. higher. But, as a rule, there are extremely small dif-
ferences in height between different lakes on the plateau-land. Only when we ap-
proach the boundaries of the plateau-land, the absolute altitude of the lakes becomes
less, the Manasarovar being at 4,602, Panggong-tso at 4,317, Jamdok-tso at 4,210,
Achik-köl at 4,250, and the Upper Kum-köl at 3,882m.