CAPTAIN RAWLING. SOUTHERN TIBET. 5 2 I
From Noll to Bal Rawling followed the same route that I did along the northern shore of the Tso-ngombo, which he calls the Tso Mo Gualari, dividing it into the sections »Tso Nyak, the twin lakes Rum Tso and Nyak Tso.» He says that it »consists of a string of five lakes Ito m. in length, the four most southern of which are fresh, and Pangong, the most northerly, salt. They are joined together by channels about 6o feet in width and 15 feet deep, the current running at nearly I V2 mile an hour.»
Rawling's paper thus abounds, as will be seen, in interesting observations. He was especially struck by the fact that all the salt lakes in the region which he traversed are now undergoing desiccation, and he gives a successful photograph of »beach-marks formed by receding water». He both mentions in his text and shows on his map mountain-ranges running meridionally, though often these ought rather to be regarded as ramifications of the main chains that stretch east and west or rather south-east and north-west. Nothing however surprised him more than finding water fresh in the Aru-tso, because Bower in 1890 found it salt and Deasy in 1896 pronounced it drinkable, that is slightly saline. The circumstance admits however of explanation in several different ways. In the first place, it is difficult to compare different people's taste in such a matter as salinity, depending as it does upon their varying standards of what constitutes drinking water. One person would pronounce water salt which another person would regard as drinkable. To one who for some time past has been accustomed to perfectly fresh spring water, the slightest flavour of salt is apt to be objectionable; on the other hand if the same man had during the same period been forced to put up with really salt water, then water with a slight tinge of salt in it would appear to be almost fresh. Properly speaking however the statements of the three travellers with regard to the water of the Aru-tso do not admit of comparison together, because they struck the shore at different places. Bower touched the lake at its northern end. Deasy's route, according to his map, ran at some distance from the western shore of the lake; but as the word »drinkable» is entered on its southern side, it is very probable that it was there that he tasted the water. And it was at the southern end of the lake that Rawling touched it. It is clear, that the salinity can vary a good deal at different places along the lake-shore; a fact that is quite evident from Rawling's own statements about Lake Markham, when he writes (as I have already cited), »The water of the lake at its western end is fresh, but as one travels towards the east the water becomes more and more impregnated . with salt, until at its eastern end it becomes undrinkable.»
I also found similar circumstances in one of the lakes of western Tibet as I have stated above. The difference may be caused by shallow passages, subaqueous ridges, and sounds. Besides, the mere fact of a brook emptying into a salt lake is enough to cause the water in the vicinity of the spot where it enters to appear fresh, owing to the fresh water spreading itself out over the salt. A somewhat similar and quite simple cause is probably the explanation of the phenomenon which gave rise to Captain Rawling's astonishment. Yet one other possibility is not precluded, namely that the water of the Aru-tso is subject to periodical changes of salinity; that is to say, that its water is sometimes salt, sometimes fresh, though this
Hedin, 7ournev in Central Asia. IV. 66
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