The surface of the country was now greatly varied, with numerous streams of water, bearing toward the east. The latter, undoubtedly, ran into those affluents of Lake Nu, or of the River of the Gazelles, concerning which M. Guillaume Lejean has given such curious details.

At nightfall, the balloon cast anchor in twenty-seven degrees east longitude, and four degrees twenty minutes north latitude, after a day's trip of one hundred and fifty miles.

CHAPTER TWENTY-FIRST.

Strange Sounds.--A Night Attack.--Kennedy and Joe in the Tree.--Two Shots.--"Help! help!"--Reply in French.--The Morning.--The Missionary. --The Plan of Rescue.

The night came on very dark. The doctor had not been able to reconnoitre the country. He had made fast to a very tall tree, from which he could distinguish only a confused mass through the gloom.

As usual, he took the nine-o'clock watch, and at midnight Dick relieved him.

"Keep a sharp lookout, Dick!" was the doctor's good-night injunction.

"Is there any thing new on the carpet?"

"No; but I thought that I heard vague sounds below us, and, as I don't exactly know where the wind has carried us to, even an excess of caution would do no harm."

"You've probably heard the cries of wild beasts."

"No! the sounds seemed to me something altogether different from that; at all events, on the least alarm don't fail to waken us."

"I'll do so, doctor; rest easy."

After listening attentively for a moment or two longer, the doctor, hearing nothing more, threw himself on his blankets and went asleep.

The sky was covered with dense clouds, but not a breath of air was stirring; and the balloon, kept in its place by only a single anchor, experienced not the slightest oscillation.

Kennedy, leaning his elbow on the edge of the car, so as to keep an eye on the cylinder, which was actively at work, gazed out upon the calm obscurity; he eagerly scanned the horizon, and, as often happens to minds that are uneasy or possessed with preconceived notions, he fancied that he sometimes detected vague gleams of light in the distance.

At one moment he even thought that he saw them only two hundred paces away, quite distinctly, but it was a mere flash that was gone as quickly as it came, and he noticed nothing more. It was, no doubt, one of those luminous illusions that sometimes impress the eye in the midst of very profound darkness.

Kennedy was getting over his nervousness and falling into his wandering meditations again, when a sharp whistle pierced his ear.

Was that the cry of an animal or of a night-bird, or did it come from human lips?

Kennedy, perfectly comprehending the gravity of the situation, was on the point of waking his companions, but he reflected that, in any case, men or animals, the creatures that he had heard must be out of reach. So he merely saw that his weapons were all right, and then, with his night-glass, again plunged his gaze into space.

It was not long before he thought he could perceive below him vague forms that seemed to be gliding toward the tree, and then, by the aid of a ray of moonlight that shot like an electric flash between two masses of cloud, he distinctly made out a group of human figures moving in the shadow.

The adventure with the dog-faced baboons returned to his memory, and he placed his hand on the doctor's shoulder.

The latter was awake in a moment.

"Silence!" said Dick. "Let us speak below our breath."

"Has any thing happened?"

"Yes, let us waken Joe."

The instant that Joe was aroused, Kennedy told him what he had seen.

"Those confounded monkeys again!" said Joe.

"Possibly, but we must be on our guard."

"Joe and I," said Kennedy, "will climb down the tree by the ladder."

"And, in the meanwhile," added the doctor, "I will take my measures so that we can ascend rapidly at a moment's warning."

"Agreed!"

"Let us go down, then!" said Joe.

"Don't use your weapons, excepting at the last extremity! It would be a useless risk to make the natives aware of our presence in such a place as this."

Dick and Joe replied with signs of assent, and then letting themselves slide noiselessly toward the tree, took their position in a fork among the strong branches where the anchor had caught.