The adventure might have had a serious termination for the lad if Joe, who had heard the collapse of the bank and the subsequent roar of the avalanche, of which the luckless Ding-dong was the centre, had not rushed to the river bank. Ding-dong, far too much astonished to raise his rifle, was standing stupidly gazing at the animal that was rushing toward him when Joe fired.

The creature gave a leap into the air, a queer kind of squeal, “like a stuck pig,” Ding-dong said afterward, and fell dead.

The shot aroused every one on the Discoverer, and they came crowding down to the river, to find Joe and Ding-dong examining, by their electric pocket lights, the carcass of a large animal with a peculiarly shaped snout. Explanations ensued, and the professor announced that it was a tapir, a species of water animal common in South America.

Matco assured them that the meat of the creature was very good eating, and much esteemed by his people, and he was permitted to cut some steaks from Joe’s prize.

“If I hadn’t ter-ter-tumbled into that pool, though, he’d have been mer-mer-mine,” declared Ding-dong positively.

“I guess you’d have been his,” laughed Joe, “that is, if you didn’t move any quicker than you were when I saw you.”

“You watch me. I’ll do something great yet,” declared Ding-dong, with a positiveness that deprived him of his stammer.

“It must have been great the way you went over that bank,” laughed Joe unfeelingly.

The professor made Ding-Dong put on dry clothes, and then the interrupted rest of the travelers was resumed. The remainder of the night passed without incident, and a breakfast that took place soon after dawn was eaten amidst much rallying of Ding-dong on his adventure of the night before.

“I’d like to have seen any of the re-re-rest of you ber-ber-brave enough to have gone near that snor-snor-snoring,” sputtered the lad, valiantly helping himself to some more tapir steak, which was found to be as good as the old Indian had declared was the case.

At eight o’clock the Discoverer was ready to resume her flight. She took the air without any accident, and under her replenished supply of gas rose with tremendous buoyancy. In fact, the descending plane had to be adjusted to keep her from shooting up too rapidly. No one on board had any desire to repeat that flight to the chilly regions of the upper air. As Ding-dong put it, “N-n-n-no more on my per-per-plate, thank you.”

“Do you think we shall sight the city to-day?” inquired Nat, as he and the professor stood on deck, just below, and in front of, the pilot house.

“Impossible to say, my lad,” was the rejoinder. “As I told you, the directions to reach it are vague in the extreme. We may have to cruise about for several days before we satisfy ourselves of its existence or non-existence.”

Nat looked disappointed. The boys, at a consultation among themselves, had about decided that that day ought to find them at their long-sought goal. Their expectation had been keyed up to such a height that delay was exasperating.

At noon the professor took his observations, and declared that, if the city existed in that part of the country, they ought to be within striking distance of it.

Excitement ran at fever heat. The boys could hardly leave the deck to eat a hasty meal. The field glasses were in constant demand. The professor announced that he would donate a handsome rifle to the first lad to spy a sign of the mystery of which they were in search.

If the boys had been eager before, this offer doubled their alertness. Ding-dong even climbed into the rigging till he was sternly ordered down by the professor.

“I thought if I got higher that I c-c-c-c-could see it s-s-s-sooner,” he explained.

“As we are now at a height of two thousand feet,” observed the professor, “I don’t think that a foot or two more of elevation would give you a very much extended view.”

It was about one-thirty when Mr. Tubbs, who was at the wheel, called the professor’s attention to something odd on the horizon. “It’s glittering,” he said, “and may be a ledge of quartz or something.”

“Can you still see it?” asked the professor.

“No,” was the rejoinder. “It just flashed up for an instant,—like a mirror in the sunlight,—and then vanished.”

“Keep a sharp lookout for its reappearance,” said the professor, with a hint of suppressed excitement in his voice.

“Shall I steer in the direction in which I last saw it?” asked the navigator of the Discoverer.

“Yes. If the old documents are correct we are so near to the location of the lost city now that any clue is worth following.”

“Then you think that the glitter may have come from the city?” asked Nat.

“I cannot say,” rejoined the professor. “It may have been that, or it may have been the sunlight flashing, for an instant, on a hidden lake.”

“But wouldn’t a lake up here come pretty near to proving the existence of the city we are in search of?” asked Nat.

“How do you draw such a conclusion?” inquired the professor, with scientific exactitude.

“I thought you said the old documents said that the lost city was on an island in a lake.”

“Ah, yes; but there may be many lakes of the kind described in these regions,” was the reply. “Any more unusual signs yet, Mr. Tubbs?” he asked presently.

“No,” was the rejoinder; but the moving picture man’s keen eyes scanned the distance like those of a hawk.

It was an hour later that Nat, who had the glasses, set them down with an excited face.

“I can see a lake!” he cried. “At least, I’m almost certain it is one.”

“Where?”

The professor’s voice had caught the infection of the boy’s excitement.

“Off there—in the same direction that Mr. Tubbs saw a glitter. I only caught a glimpse of it, but it looked as if there was the glint of water in among those queer, sharp-pointed peaks off there.”

“Speed up the engine if you can, Master Bell,” said the professor, with an expression in his voice that the boys had never heard there before.

“We must investigate this at once and lose no time,” he went on. “The old documents say that the lost city is on an island in a lake set in the midst of mountains, over which there is no way of climbing but by the lost and secret roads of the Incas.”

“I guess you get the rifle, Nat,” said Joe, without a trace of envy in his voice, though.

“I w-w-w-wish I’d s-s-seen it f-f-first,” sputtered Ding-dong, who was leaning far out over the rail.

“You’d have shot a tapir with the rifle, I suppose,” scoffed Joe.

“No; I’d have shot a-a——”

“Good heavens!” cried the professor, as both Nat and Joe sprang forward.

The abrupt conclusion of the stuttering boy’s speech had been caused by the fact that, as he made it, he half turned, and losing his balance plunged over the rail.

The Discoverer was then nineteen hundred and fifty feet above the surface of the earth!