And Joe, picking up one more block, desperately tossed it out of the car. The balloon rose a hundred feet or so, and, aided by the cylinder, soon passed above the surrounding summits.

"Now, Joe," resumed the doctor, "there still remains a handsome fortune for you; and, if we can only keep the rest of this with us until the end of our trip, there you are--rich for the balance of your days!"

Joe made no answer, but stretched himself out luxuriously on his heap of quartz.

"See, my dear Dick!" the doctor went on. "Just see the power of this metal over the cleverest lad in the world! What passions, what greed, what crimes, the knowledge of such a mine as that would cause! It is sad to think of it!"

By evening the balloon had made ninety miles to the westward, and was, in a direct line, fourteen hundred miles from Zanzibar.

CHAPTER TWENTY-FOURTH.

The Wind dies away.--The Vicinity of the Desert.--The Mistake in the Water-Supply.--The Nights of the Equator.--Dr. Ferguson's Anxieties. --The Situation flatly stated.--Energetic Replies of Kennedy and Joe. --One Night more.

The balloon, having been made fast to a solitary tree, almost completely dried up by the aridity of the region in which it stood, passed the night in perfect quietness; and the travellers were enabled to enjoy a little of the repose which they so greatly needed. The emotions of the day had left sad impressions on their minds.

Toward morning, the sky had resumed its brilliant purity and its heat. The balloon ascended, and, after several ineffectual attempts, fell into a current that, although not rapid, bore them toward the northwest.

"We are not making progress," said the doctor. "If I am not mistaken, we have accomplished nearly half of our journey in ten days; but, at the rate at which we are going, it would take months to end it; and that is all the more vexatious, that we are threatened with a lack of water."

"But we'll find some," said Joe. "It is not to be thought of that we shouldn't discover some river, some stream, or pond, in all this vast extent of country."

"I hope so."

"Now don't you think that it's Joe's cargo of stone that is keeping us back?"

Kennedy asked this question only to tease Joe; and he did so the more willingly because he had, for a moment, shared the poor lad's hallucinations; but, not finding any thing in them, he had fallen back into the attitude of a strong-minded looker-on, and turned the affair off with a laugh.

Joe cast a mournful glance at him; but the doctor made no reply. He was thinking, not without secret terror, probably, of the vast solitudes of Sahara--for there whole weeks sometimes pass without the caravans meeting with a single spring of water. Occupied with these thoughts, he scrutinized every depression of the soil with the closest attention.

These anxieties, and the incidents recently occurring, had not been without their effect upon the spirits of our three travellers. They conversed less, and were more wrapt in their own thoughts.

Joe, clever lad as he was, seemed no longer the same person since his gaze had plunged into that ocean of gold. He kept entirely silent, and gazed incessantly upon the stony fragments heaped up in the car--worthless to-day, but of inestimable value to-morrow.

The appearance of this part of Africa was, moreover, quite calculated to inspire alarm: the desert was gradually expanding around them; not another village was to be seen--not even a collection of a few huts; and vegetation also was disappearing. Barely a few dwarf plants could now be noticed, like those on the wild heaths of Scotland; then came the first tract of grayish sand and flint, with here and there a lentisk tree and brambles. In the midst of this sterility, the rudimental carcass of the Globe appeared in ridges of sharply-jutting rock. These symptoms of a totally dry and barren region greatly disquieted Dr. Ferguson.

It seemed as though no caravan had ever braved this desert expanse, or it would have left visible traces of its encampments, or the whitened bones of men and animals. But nothing of the kind was to be seen, and the aeronauts felt that, ere long, an immensity of sand would cover the whole of this desolate region.