In the spring of the year 1905 my mind was much occupied with thoughts of a new journey to Tibet. Three years had passed since my return to my own country; my study began to be too small for me; at eventide, when all around was quiet, I seemed to hear in the sough of the wind a voice admonishing me to “come back again to the silence of the wilderness”; and when I awoke in the morning I involuntarily listened for caravan bells outside. So the time passed till my plans were ripened and my fate was soon decided; I must return to the freedom of the desert and hie away to the broad plains between the snow-clad mountains of Tibet. Not to listen to this secret voice when it speaks strongly and clearly means deterioration and ruin; one must resign oneself to the guidance of this invisible hand, have faith in its divine origin and in oneself, and submit to the gnawing pain which another departure from home, for so long a time and with the future uncertain, brings with it. In the concluding lines of my scientific work on the results of my former journey (Scientific Results) I spoke of the impossibility of giving a complete description of the internal structure of Tibet, its mountains and valleys, its rivers and lakes, while so large a part of the country was still quite unknown. “Under these circumstances,” I said (vol. iv. p. 608), “I prefer to postpone the completion of such a monograph till my return from the journey on which I am about to start.” Instead of losing myself in conjectures or arriving at confused results owing to lack of material, I would rather see with my own eyes the unknown districts in the midst of northern Tibet, and, above all, visit the extensive areas of entirely unexplored country which stretches to the north of the upper Brahmaputra and has not been traversed by Europeans or Indian pundits. Thus much was à priori certain, that this region presented the grandest problems which remained still unsolved in the physical geography of Asia. There must exist one or more mountain systems running parallel with the Himalayas and the Karakorum range; there must be found peaks and ridges on which the eye of the explorer had never lighted; turquoise-blue salt lakes in valleys and hollows reflect the restless passage of the monsoon clouds north-eastwards, and from their southern margins voluminous rivers must flow down, sometimes turbulent, sometimes smooth. There, no doubt, were nomad tribes, who left their winter pastures in spring, and during the summer wandered about on the higher plains when the new grass had sprung up from the poor soil. But whether a settled population dwelt there, whether there were monasteries, where a lama, punctual as the sun, gave the daily summons to prayer from the roof by blowing through a shell,—that no one knew. Tibetan literature, old and recent, was searched in vain for information; nothing could be found but fanciful conjectures about the existence of a mighty chain, which were of no value as they did not accord with the reality and were not based on any actual facts. On the other hand, a few travellers had skirted the unknown country on the north and south, east and west, myself among the number. Looking at a map, which shows the routes of travellers in Tibet, one might almost suppose that we had purposely avoided the great white patch bearing on the recently published English map only the word “Unexplored.” Hence it might be concluded that it would be no easy feat to cross this tract, or otherwise some one would ere now have strayed into it. In my book Central Asia and Tibet I have fully described the desperate attempts I made in the autumn and winter of 1901 to advance southwards from my route between the Zilling-tso and the Pangong-tso. One of my aims was to find an opportunity of visiting one or more of the great lakes in Central Tibet which the Indian pundit, Nain Sing, discovered in 1874, and which since then had never been seen except by the natives. During my former journey I had dreamt of discovering the source of the Indus, but it was not then my good fortune to reach it. This mysterious spot had never been inserted in its proper place on the map of Asia—but it must exist somewhere. Since the day when the great Macedonian Alexander (in the year 326 B.C.) crossed the mighty stream with his victorious host, the question of the situation of this spot has always stood in the order of the day of geographical exploration.