"A mirage!" exclaimed Dan with a catch in his voice. "So that's why we seemed to be getting farther away from that green spot all the time. But Dick, are you certain? I'd have sworn it was the real thing."
But even as they talked, Dan noticed the thinning haze ahead. It seemed to be rising and soon disappeared into the sky.
"Say, Dick, when did you catch on?" asked Dan.
"About five minutes ago. How am I going to explain it to them? They may never have seen one and may think that it is black magic. See, the caravan has vanished, too."
"Tell them it's Cimbula out there," said Dan with a laugh. "They'll believe that, all right."
While the boys were talking, the haze dissolved completely, leaving a far stretch of sandy waste.
"Ah-woe Tahara!" moaned Raal touching Dick's arm. "Look ahead. The spirit of evil has swallowed up the oasis. It is a warning, O Master. I have seen it many times before."
Dick gave a sigh of relief. At least the mirage was not unknown to the tribesmen.
"A warning, what do you mean, Raal?" asked Dick.
"Thus comes the oasis on the desert at times, leading men to destruction. Warriors depart to take possession of the new land and find themselves without food and drink. They ride around in circles in order to find the green oasis. Then at last the demons gobble them up. Did you not see the caravan disappear? It is a bad omen, so say my people."