Joe told of seeing the phenomenon from the top of the hill, saying that there appeared to be at least five hundred horsemen coming toward them.
When he had finished, the naturalists and Dr. Kirshner jumped up in wonder and not a little fear, but Fekmah only laughed.
“W-what’s humorous!” demanded Mr. Lewis, greatly perplexed.
“Everything,” said Fekmah, laughing still harder. “What the young men saw was only an illusion or mirage. There no army on Sahara. Only look like army.”
“You mean it was a trick of nature, like the more common mirages of lakes on the desert?” asked Dr. Kirshner with great interest.
“Yes,” the Arab answered. “Caused by the bending of the rays of light when they strike the hot sand.”
“Well, that’s a new one on me!” confessed Bob. “I was aware of the fact that mirages of lakes are common, but that I should see an army——”
It was now rapidly becoming dark. The explorers thought it best to sleep all through the night and not wait for the moon, for they greatly needed the rest.
“Tomorrow morning I’d like to see that mirage that you boys thought was an army,” said Mr. Holton, when they prepared to retire.