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0249 Southern Tibet : vol.2
南チベット : vol.2
Southern Tibet : vol.2 / 249 ページ(白黒高解像度画像)

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doi: 10.20676/00000263
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CHAPTER XXV.

THE OSCILLATIONS IN THE WATER-LEVEL OF THE
LAKES.

In the preceding chapters I have tried to give a *resumé* of the history of ex-
ploration in the region of the Manasarovar and the Rakas-tal, and I have especially
tried to bring together as many records as possible about the connection between
the lakes and between the western lake and the Satlej. In the latter respect the
result has not been encouraging. For, as a rule, the earlier records are either
unreliable, or, even if they seem to be reliable as regards facts, they do not allow
us to fix the date of the observations. The only exception from this is the Lama
survey. Then follows a century with uncertain information, and only with Moor-
croft do we enter upon solid ground.

The problem is, however, one of very great interest. In itself it is not of great
importance whether water at a certain period flowed out of the lakes or not. Only
on account of the bright light it spreads over the oscillations in the last, or present,
climatic period, does the question become important. But even during the last century
the records are very few, and at any rate insufficient to make it possible to follow
the periodicity of the curve. This should not be surprising, for it may even be
difficult to arrive at reliable conclusions when comparing old maps and descriptions
of lakes and rivers in Europe with the present state of things. How much more
difficult must it then be to study the oscillations in a couple of Tibetan lakes, which
only a hundred years ago were visited by the first scientifically trained European,
and since his time have been seen by only a very few reliable visitors.

And still these two lakes present us with a most excellent and sensitive in-
strument for measuring the changes in the climate, especially the precipitation. The
instrument is there, but its records have only in a very few cases been read and
understood. With great patience and trouble the glacial geologists have tried to
interpret the silent story told by the old front moraines of Himalayan glaciers to
find out the advance and retreat of the ice streams. The general result at which
they have arrived may be expressed in the following words by Guy E. Pilgrim: