time after I first came in sight of it, I felt confident that it was indeed full of water. Then across this flat, unruffled surface came sweeping what appeared to be a number of waterspouts, tall, perfectly defined columns, travelling rapidly. But they were not water, but sand-whorls, a common enough phenomenon in these dry regions, and known to the Boers as _zand-duivels_ (sand-devils), and which, beginning with a slight whorl of sand, gather force and velocity as they travel, picking up small pebbles, sticks, leaves, and every light article that comes in their path, and bearing it aloft to a tremendous height. Here on this perfectly flat floor there was nothing to break their symmetry, and they were as well-defined as the waterspouts I took them for. From the high dunes from which we first obtained a full view of the pan, the whole circuit of its flanking dunes was plainly visible, but as we descended the mirage hid these, and when we eventually stood on the floor no sign of the far dunes could be seen: we were apparently standing on the edge of a vast unbroken lake, whose mirror-like surface reflected the clouds as faithfully as a sheet of water would have done. And when, after a few minutes, several more “waterspouts” sprang up and went sailing across the “water,” I had almost to pinch myself; the whole thing was so real in its unreality. The pan is about two miles wide by five miles long, but by the time we were half-way the mirage had puzzled us so that we began to wonder if ever we should find the pits we were looking for. Occasionally a dune on the far bank loomed up as though it _might_ be a solid reality, but a few steps in that direction would see it melt away, dissolving into the hazy shimmer. It was impossible to judge either distance or proportion; on several occasions a big pile of rocks came into view apparently as large as cottages and half a mile away, and, on our making for them, proved to be boulders the size of a bucket, and barely fifty yards’ distance. Then a long line of gemsbok came into sight following each other at perfectly regular intervals. Suddenly they stopped as one, then they all tossed their heads together, and then the line began to waver and break up and float away, and lo! there stood a solitary old bull staring at us, quite alone--the rest had all been tricks of the mirage. When we were within thirty yards he turned and made off, and was soon up to his knees in water, apparently, and followed by several of his spectral attendants. Altogether the place seemed absolutely uncanny, and in no part of the Kalahari have I ever seen the mirage play such tricks as at Aar Pan.