In this inflamed atmosphere the heat appeared to vibrate as it does above a blazing hearth, while the mind grew desperate in contemplating the limitless calm, and could see no reason why the thing should ever end, since immensity is a species of eternity.

Thus, at last, our hapless travellers, deprived of water in this torrid heat, began to feel symptoms of mental disorder. Their eyes swelled in their sockets, and their gaze became confused.

When night came on, the doctor determined to combat this alarming tendency by rapid walking. His idea was to pace the sandy plain for a few hours, not in search of any thing, but simply for exercise.

"Come along!" he said to his companions; "believe me, it will do you good."

"Out of the question!" said Kennedy; "I could not walk a step."

"And I," said Joe, "would rather sleep!"

"But sleep, or even rest, would be dangerous to you, my friends; you must react against this tendency to stupor. Come with me!"

But the doctor could do nothing with them, and, therefore, set off alone, amid the starry clearness of the night. The first few steps he took were painful, for they were the steps of an enfeebled man quite out of practice in walking. However, he quickly saw that the exercise would be beneficial to him, and pushed on several miles to the westward. Once in rapid motion, he felt his spirits greatly cheered, when, suddenly, a vertigo came over him; he seemed to be poised on the edge of an abyss; his knees bent under him; the vast solitude struck terror to his heart; he found himself the minute mathematical point, the centre of an infinite circumference, that is to say--a nothing! The balloon had disappeared entirely in the deepening gloom. The doctor, cool, impassible, reckless explorer that he was, felt himself at last seized with a nameless dread. He strove to retrace his steps, but in vain. He called aloud. Not even an echo replied, and his voice died out in the empty vastness of surrounding space, like a pebble cast into a bottomless gulf; then, down he sank, fainting, on the sand, alone, amid the eternal silence of the desert.

At midnight he came to, in the arms of his faithful follower, Joe. The latter, uneasy at his master's prolonged absence, had set out after him, easily tracing him by the clear imprint of his feet in the sand, and had found him lying in a swoon.

"What has been the matter, sir?" was the first inquiry.

"Nothing, Joe, nothing! Only a touch of weakness, that's all. It's over now."

"Oh! it won't amount to any thing, sir, I'm sure of that; but get up on your feet, if you can. There! lean upon me, and let us get back to the balloon."

And the doctor, leaning on Joe's arm, returned along the track by which he had come.

"You were too bold, sir; it won't do to run such risks. You might have been robbed," he added, laughing. "But, sir, come now, let us talk seriously."

"Speak! I am listening to you."

"We must positively make up our minds to do something. Our present situation cannot last more than a few days longer, and if we get no wind, we are lost."

The doctor made no reply.

"Well, then, one of us must sacrifice himself for the good of all, and it is most natural that it should fall to me to do so."

"What have you to propose? What is your plan?"

"A very simple one! It is to take provisions enough, and to walk right on until I come to some place, as I must do, sooner or later. In the mean time, if Heaven sends you a good wind, you need not wait, but can start again. For my part, if I come to a village, I'll work my way through with a few Arabic words that you can write for me on a slip of paper, and I'll bring you help or lose my hide. What do you think of my plan?"

"It is absolute folly, Joe, but worthy of your noble heart. The thing is impossible. You will not leave us."

"But, sir, we must do something, and this plan can't do you any harm, for, I say again, you need not wait; and then, after all, I may succeed."

"No, Joe, no! We will not separate. That would only be adding sorrow to trouble.