Before leaving Kalliboas that day we walked with him along the eastern margin of the lake, and came to a tall circular tower in white marble, which was visible from a considerable distance away. We ascended this by an inner stairway and at last stood upon the roof, where we found a sentinel and one of the most ingenious devices imaginable. The platform was surrounded by a parapet about breast-high, topped by a continuation in some transparent pebble-like rock, while outside this was a similar parapet in the same material, the two arranged so as to act as a continuous telescope. How the difficulty of varying focus was overcome I couldn't understand, but the fact remains that in whatever direction we looked the surrounding valleys and foothills--even the upper slopes of the mountains themselves--seemed amazingly near to us. The words of Kalliboas sounded behind us in a sort of grim caress. 'See now, strangers,' he said, 'is it even as the student told when he cast his mind out over the valley?' Poyning was staring southward. 'There are men,' he said in a queer voice. 'What do they do?' 'They build a wall to protect the tomb. Since the great snow fell, new streams have burst out of the mountains in that quarter. Our engineers are busy with works to direct the water down to the lake by channels where it shall not injure the crops of our valley. Now it flows lawlessly, and though the tomb which you see is founded in solid rock, we have judged it wise to build the protecting wall.' Poyning remained staring through the crystal for some time, particularly towards the tomb and the direction from which we ourselves had entered the valley. I imagine we were both thinking that probably from this tower our first approach was signalled; and I know I was wondering how it came about, since a watcher was apparently posted here always, that the approach of the Tibetan, Sbrang Chikya, could have escaped observation.