them?” Johnny asked.

“Who knows?” There was a suggestion of deep mystery in his companion’s tone. “That’s the thrill and charm that comes from exploring the sea’s depths! Anything may put in an appearance. Creatures such as the world never has dreamed of, may pass before our eyes!”

“How strange! How sort of—”

Johnny broke off to stare, then to exclaim—“There—there’s something huge!”

“Quick! The camera!” Dave’s voice trembled. “No—it’s too late!”

Moving with surprising swiftness, some great, dark bulk passed through the outer edge of their narrow beam of light.

“Wha—what was it?” Johnny felt a little giddy.

“Some huge creature of the deep. Perhaps a whale or a black fish,” Dave replied quietly. “It is known that they penetrate to these depths. Then again—perhaps it was some huge, scaly creature that inhabits these depths alone.”

“What if it had collided with us, or tangled in our cable?”

“Then,” Dave’s tone was dry and droll, “we might have taken a long, swift ride through space!”

“Swinging like a pendulum?”

“That’s it! On our thousands of feet of cable.”

“I shouldn’t like that,” Johnny shuddered.

“Then why bring it up?” Dave chuckled.

“Why, indeed!” Johnny laughed—

After another half hour of waiting, for one more fascinating spectacle, Dave decided to signal for their return to the top. Johnny experienced a real sense of relief.

“To explore the depths of the sea—earth’s last great frontier—this is our purpose,” Dave said, as they began to rise. “For centuries men have been discovering strange creatures washed up on beaches. They could have come from nowhere save the ocean depths. For many years they have been dragging these depths with nets, to discover, if they could, what lived in these ‘spooky waters’ of dense darkness.”

And now, Johnny thought exultantly, I am having a part in an expedition that may reveal the secrets of these dark depths.

But once again his mind returned to Samatan. This strange person, with his apparent hold on the native crew, was cook for the expedition. And a marvelous cook he was. Johnny had been interested in the strange old man, from the first. He had studied him carefully. And there could be no mistake about it—Samatan was endeavoring to stir the crew to something....

Now the blue-black world about him appeared to be changing color. The blackness was less intense.

“It’s like the coming of dawn,” he said to Dave.

“Yes,” Dave chuckled, “only here we may make our own dawn, slow or fast, as we choose!”

That this was to be rather a fast dawn, Johnny was not long in discovering. But it was fascinating. To pass from inky blackness to dark, deep blue, on into colors that resembled a sunrise, and then to the eternal blue of a bright, tropical day, was an experience not soon to be forgotten. From time to time as they rose, strange denizens of the sea seemed to peer at them. Once a shark shot past, and just before they reached the top, a great turtle swam awkwardly away.

Came the bump—bump of their steel ball as, lifted by the great crane, it landed on the deck. Then, almost before he knew it, Johnny thrust his head into bracing fresh air, to be greeted by a smiling face and to hear a girl’s voice saying:

“Hello, Johnny Thompson! How do you like being down in Davey Jones’ locker?”

After assuring her of his enthusiasm, Johnny hurried to his stateroom. He was wondering whether Doris remembered their “secret” of the night before.

CHAPTER III
A BRIGHT EYED BEACH-COMBER

Johnny went at once to a darkroom that had been quickly prepared in the hold. Pictures could be taken on land in what appeared to be complete darkness; he knew this from his work with Lee Martin. But would the utter blackness beneath the sea be the same? He would know, soon.

He watched the films with absorbed interest. As the developer took hold, he saw nothing but blackness.

“Nothing there!” he muttered disappointedly. “Wasted shots. We—”

But wait! Was something coming out? Yes! There it was! An indistinct, shadowy form!

His thoughts leaped ahead. His pictures were to be a success. He would be asked, times without number, to go down in that darkness and take more pictures. Dangerous work, but he had to be a good sport, and besides, it was splendid experience for him.

The strange, undersea creatures, some very large, with heads as long as their bodies, with fantastic buck teeth and hideous eyes, some small and snakelike and some as normal looking as any fish to be found near the surface, came out clearly visible on the film.

“Perfect!” was the professor’s enthusiastic reaction when Johnny showed him damp prints a few hours later. “A real contribution! And you took them in complete darkness!”

“In what appeared to be complete darkness,” Johnny corrected. “I did it with an infra-red light screen. That screen shuts out all but the infra-red rays. Eyes can’t see the light of these rays.

“Of course,” he went on, “we might have used a flood light, but that would have frightened those creatures away. As it is, we got them in what you might call a natural pose. Candid camera shots from the deep sea,” he laughed.

“Yes, yes,” the professor agreed. “Very remarkable and most useful!”

“Of course,” said Johnny, with a touch of modesty. “I learned all this from Lee Martin. He took me on as a helper and sort of body-guard. I just absorbed this camera stuff as we went along.”

“I see,” said the professor, “that you have learned one of the real secrets of success.”

“What’s that?” Johnny asked.

“To learn all you can about everything that comes your way, and to file that knowledge away in your brain. One never can tell when the opportunity to use such information may come to him. Perhaps never, but it’s always there!

“You should be a great aid to us,” the professor added thoughtfully. “You see,” he said, leaning forward in his chair, “I regard this work as the most interesting and exciting of my entire career. Young man,”—his eyes fairly shone, “what place do you think of as our last frontier?”

Then, before Johnny could reply—“You may go east, west, north, south” the professor continued “but you find no frontier. You must go up or down! Up into the stratosphere—or down, into the sea. These are our last frontiers. Dave and I have chosen the deep sea, because there we may yet discover forms of life not known to man. These pictures,” he held them up, “show two types of fish never before seen—and we have but begun!”

* * * * * * * *

“We have but begun,” Johnny repeated softly to himself as, some hours later, he once more paced the deck in his solitary vigil. “We have begun. Where shall we end? We—”

His soliloquy was interrupted. Had he caught a gleam out there on the water? He thought so. Now it was gone.

That was one thing he was to watch for—natives in dugouts and canoes. Who could tell what they might do? In a strange land one did well to keep close watch. He would keep an eye out for that light....

“Exploring our last frontier,” he whispered softly. He was in for something truly big