On the 21st we found that the delegates had decamped in the night. Perhaps, after all, I had made a mistake, and allowed these very coy birds to escape just as they had come into my hand. On the whole I thought not. I believed others would soon come in. So I marched very contentedly along the shores of one of the most beautiful lakes I have ever seen—the Yamdok Tso. It was 14,350 feet above sea-level. In shape it was like a rough ring, surrounding what is practically an island; and in colour it varied to every shade of violet and turquoise blue and green. At times it would be the blue of heaven, reflecting the intense Tibetan sky. Then, as some cloud passed over it, or as, marching along, we beheld it at some different angle, it would flash back rays of the deep greeny-blue of a turquoise. Anon it would show out in various shades of richest violet. Often, when overhead all was black with heavy rain-clouds, we would see a streak of brilliant light and colour flashing from the far horizon of the lake; while beyond it and beyond the bordering mountains, each receding range of which was of one more beautiful shade of purple than the last, rose once more the mighty axial range of the Himalayas, at that great distance not harsh in their whity coldness, but softly tinted with a delicate blue, and shading away into the exquisite azure of the sky. What caused the marvellous colouring of this lake, which even the Tibetans call the Turquoise Lake, we could none of us say. Perhaps it was its depth, perhaps it was its saline character, or some chemical component of its water. But whatever the main cause, one cause at least must have been the intense blue of the Tibetan sky at these great altitudes, so deep and so translucent that even the sky of Greece and Italy would pale beside it.
This latter theory is what Lord Rayleigh would adopt. In a lecture which he delivered this year at the Royal Institution on the causes of the coloration of water, he gave his conclusion, from careful observations and tests, that the cause of the blueness of, say, the Mediterranean Sea was the Mediterranean sky, which was exactly the theory we had thought must apply to this Tibetan lake.
Marching along by this lake we had much rain, turning into snow at night. Pete Jong, a picturesque little fort close to the shore, was reached on the 22nd, where, as at Nagartse, a company of infantry and a few mounted infantry were left to keep up the line of communications. From here the mounted infantry, reconnoitring ahead, reported the remnants of the Kham force to be retreating in a disorganized condition, and looting the country _en route_.