“All right,” said Bob. “I’m off.” And he started away to the left. With a wave of the hand, Jack set out to the right, little dreaming of the momentous events to occur before he saw Bob again. CHAPTER VIII. BOB’S FIGHT AGAINST ODDS. As Bob rode along on camel-back in the lee of the sand dunes, there was never a thought of danger in his mind. The Sahara is not like the great grassy steppes of Siberia or the plains of western America, which are flat and level as a table top and across which one can see for miles in every direction. On the contrary, this great African desert is filled with shifting sand dunes, low hills of sand, which are whipped away when the strong winds blow and change their position, piling up in new drifts. In appearance it was now to Bob’s eye like the sea when waves were kicking up. In the trough of these sandy waves he made his way forward, exercising care in advancing from the shelter of one dune to another to keep below the crests. It was lonesome riding, under the baking sun, in that land of stillness, without sign nor sound of any human being. He had an eerie feeling, as if something were about to happen. But he shook this off, and laughed at himself. Merely a touch of nerves, he thought, due to the loneliness of the surroundings. Before setting out, it had been decided he and Jack would have to ride a good half hour away from their starting point, from the place where Ali was posted, before they would be in the proper position. Therefore, looking at his watch now and again, he kept on without exposing himself to gain sight of the ostrich herd, until the full half hour had elapsed. It seemed to him a much longer time, and if it had not been for his watch he would have been tempted several times to clamber up a sand dune and look around. When at length, the allotted time having elapsed, he did urge his camel up the top of the nearest sand dune, there was no sign either of ostriches or of his companions. Far in the distance could be seen the tops of the palm trees of the oasis, dwarfed and beautiful as a painting against the blue sky. All else was hidden from his sight. “Shucks,” thought Bob, “in dodging to keep below the tops of the sand hills, I must have gotten off my course.” That, in reality, was what had occurred. Instead of the small circle he had planned to make, which would have put him on the point of an arc a third of the way around the herd from Ali’s station, he had borne off the course gradually but surely in his attempts to remain hidden. Moreover, he had gotten into a region of larger sand dunes, so big they amounted to low hills.