"But these storms change about so, Excellency," said the Sheikh. "This may suddenly turn back or rush off right away from us. It will, I think, go onward towards the great river away to our left, and sweep across it. No!" he thundered out. "Be ready; it comes," for suddenly a hot blast of air smote the party, fluttering their robes, and the whirling pillars, so distinct and clear a few minutes before, grew misty as if seen through a dense haze; for by one of its sudden changes the storm had swept round almost at right-angles, and the next minute the sky was obscured, the camels were groaning as they buried their heads in the loose sand, and the storm of hot, suffocating dust, borne on a mighty wind, was upon them, shrieking, tearing at everything loose, and buffeting its victims, who could hardly breathe, the dust choking every tiny crevice in the cotton cloth held over the face. The roar and rush were horrible, the confusion of intellect strange and peculiar, and Frank, as he cowered down behind his camel with his forehead pressed against the saddle to keep his veil in its place, felt as if he were breathing the scorching air out of some open furnace door, while the choking, irritating sensation in the air-passages seemed as if it must soon terminate in death. Doubtless that would have been their fate if the storm had lasted; but as quickly as it had come upon them it passed over, and in a few minutes the air about them was clear again, the sky blue, and the sun beating down, while the dust-cloud pillars were careering along, distinctly seen a quarter of a mile away. "Yes," said the Sheikh calmly, "they are terrible, these hot whirlwinds. Their Excellencies would be glad to bathe and clear their faces and hair from the thick dust, but there is no water save for drinking. We have never had a worse one than this, Excellency, in our travels." "Never," said the professor, who knelt in the sand trying to clear his eyes from the impalpable brownish dust, "and I don't want to meet another. This is one of the experiences of a desert journey, Frank. Why, lad, you are turned from black to brown." "And you the same, but from white," replied Frank, smiling. "I suppose so. It's bad for the Hakim's white robes, too. I say, Ibrahim, when shall we strike the river?" "Not for many days, Excellency; but we shall halt at fountains among the rocks."