"They are apes," said Joe, "imitating us."

"It means," said the doctor, laughing, "that it is you, Dick, yourself, making that signal to yourself; or, in other words, that we see ourselves in the second balloon, which is no other than the Victoria."

"As to that, master, with all respect to you," said Joe, "you'll never make me believe it."

"Climb up on the edge of the car, Joe; wave your arms, and then you'll see."

Joe obeyed, and all his gestures were instantaneously and exactly repeated.

"It is merely the effect of the MIRAGE," said the doctor, "and nothing else--a simple optical phenomenon due to the unequal refraction of light by different layers of the atmosphere, and that is all.

"It's wonderful," said Joe, who could not make up his mind to surrender, but went on repeating his gesticulations.

"What a curious sight! Do you know," said Kennedy, "that it's a real pleasure to have a view of our noble balloon in that style? She's a beauty, isn't she?-- and how stately her movements as she sweeps along!"

"You may explain the matter as you like," continued Joe, "it's a strange thing, anyhow!"

But ere long this picture began to fade away; the clouds rose higher, leaving the balloon, which made no further attempt to follow them, and in about an hour they disappeared in the open sky.

The wind, which had been scarcely perceptible, seemed still to diminish, and the doctor in perfect desperation descended toward the ground, and all three of the travellers, whom the incident just recorded had, for a few moments, diverted from their anxieties, relapsed into gloomy meditation, sweltering the while beneath the scorching heat.

About four o'clock, Joe descried some object standing out against the vast background of sand, and soon was able to declare positively that there were two palm-trees at no great distance.

"Palm-trees!" exclaimed Ferguson; "why, then there's a spring--a well!"

He took up his glass and satisfied himself that Joe's eyes had not been mistaken.

"At length!" he said, over and over again, "water! water! and we are saved; for if we do move slowly, still we move, and we shall arrive at last!"

"Good, master! but suppose we were to drink a mouthful in the mean time, for this air is stifling?"

"Let us drink then, my boy!"

No one waited to be coaxed. A whole pint was swallowed then and there, reducing the total remaining supply to three pints and a half.

"Ah! that does one good!" said Joe; "wasn't it fine? Barclay and Perkins never turned out ale equal to that!"

"See the advantage of being put on short allowance!" moralized the doctor.

"It is not great, after all," retorted Kennedy; "and if I were never again to have the pleasure of drinking water, I should agree on condition that I should never be deprived of it."

At six o'clock the balloon was floating over the palm-trees.

They were two shrivelled, stunted, dried-up specimens of trees--two ghosts of palms--without foliage, and more dead than alive. Ferguson examined them with terror.

At their feet could be seen the half-worn stones of a spring, but these stones, pulverized by the baking heat of the sun, seemed to be nothing now but impalpable dust. There was not the slightest sign of moisture. The doctor's heart shrank within him, and he was about to communicate his thoughts to his companions, when their exclamations attracted his attention. As far as the eye could reach to the eastward, extended a long line of whitened bones; pieces of skeletons surrounded the fountain; a caravan had evidently made its way to that point, marking its progress by its bleaching remains; the weaker had fallen one by one upon the sand; the stronger, having at length reached this spring for which they panted, had there found a horrible death.

Our travellers looked at each other and turned pale.

"Let us not alight!" said Kennedy, "let us fly from this hideous spectacle! There's not a drop of water here!"

"No, Dick, as well pass the night here as elsewhere; let us have a clear conscience in the matter.