Signal bells clanged, and again they were gliding under the ocean's armor of ice.

As he listened to the hum of the machinery, one question puzzled Dave. He had seen something along the end of that ice-floe. What was it? A sail?

If so, it was a very strange one--half white and half black. He could not be sure it was a sail. But what else could it have been?

But now they had swept out from under the ice. It was time to rise.

Instantly he pressed the b.u.t.ton. The craft slowed again. Another press, and as before they rose. This time no white surface would interrupt them.

A current coming from land caught them forward and tilted the craft. She slanted from fore to aft. This did not matter; she would right herself on the surface like a cork.

But what was this? As the point shot from the water, something rang out against the steel. This was followed immediately by what, in the narrow apartments, amounted to a deafening explosion; then came the sound of rushing waters.

"Great G.o.d! We're bombed!" shouted the Doctor.

Dave's cool head saved them for the moment. His hand seized an electric switch and he pulled it desperately. The bow compartment was quickly closed, checking the rush of water into the rest of the "sub,"

Fortunately, no one had been forward at the time.

But now they were sinking rapidly. Then came the throb of the pumps forcing out the water from the compartments aft. Slowly the sickening sinking of their ship was checked.

"Will she rise again?" asked the Doctor, white-faced but cool.

"I think so, sir," responded Dave.

Dave watched a gauge with anxious eyes. The pumps were still working.

Would the craft stand the test? Would she rise?

One, two, three minutes he watched the dial; then a fervent "Thank G.o.d!"

escaped his lips. The sub was rising again.

But once more his brow was clouded. What awaited them on the surface?

"One more," he muttered, "just one more, and we are done for."

Every man aboard the submarine had a different explanation for the bomb which had disabled their craft. Jones, the electrician, had just finished reading the adventures of a young British gunner in these very waters somewhere back in the eighties. The story had to do with the defense of seal fisheries against the j.a.ps, and Jones was sure that a j.a.panese seal-poaching boat had bombed them. McPherson, who had seen active service chasing German subs, was certain they had encountered one of the missing U boats. Wilder believed it had been a Russian cruiser, and, of course, Jarvis blamed it to the "bloomin' 'eathen."

The first and third of these theories could be discarded at once, since no craft was to be seen when last they submerged, and a cruiser or schooner of any size could scarcely have escaped their attention.

As for Dave, he had another theory, but was too busy to talk about it. He had read a great deal regarding the Eskimos and their methods of hunting.

Meanwhile the submarine was rising slowly toward the surface. She was coming up with her stern tilted high this time, for the water in her forward compartments disturbed her balance. Every heart beat fast as the water above grew lighter.

"McPherson, be ready to throw open the hatch the minute we are clear,"

commanded Dave. "All life belts on?" he asked.

"Aye, aye, sir!" came in chorus.

"Rifles?"

"At hand, sir."

"Ready then."

There came a sudden burst of light, the creak of hinges, the thud of the hatch, then the thud of feet as the men rushed for the deck.

In another moment the crew found themselves outside clinging to the tilted and unsteady craft, blinking in the sunlight, and seeing--?

Princ.i.p.ally white ice and dark water. Off in the distance, indeed, was an innocent-looking native skin-boat. There were, perhaps, ten natives aboard.

"Thought so," chuckled Dave.

"You thought what?" demanded the Doctor. Every eye was turned on the young commander.

"Thought we'd been shot by natives with a whale-gun. Took us for a whale, don't you see? Whale-gun throws a bomb that explodes inside the whale and kills him. In this case, it exploded against us and raised the very old d.i.c.kens. Here they come. You'll see I'm right."

And he was right. The crew of christianized natives were soon alongside, very humble in their apologies, and very anxious to a.s.sist in undoing the damage they had wrought.

"Have we any extra steel plate?" asked the Doctor.

"Yes, sir. Have to be shaped, though," replied Dave.

"Can we do it?"

"I think so, on sh.o.r.e."

"All right, then. Get these natives to give us a hand and we'll go on the sand-bar for repairs. Bad cess to the whaling industry of the Eskimos!

It's lost us a full two days, and perhaps the race! But we must not give up. Things can happen to airplanes, as well."

It took a hard half-day's work to bring the craft to land, but at last the task was done and the mechanics were hammering merrily away on the steel with acetylene torch sputtering, and forty natives standing about open-mouthed, exclaiming at everything that happened, and offering profound explanations in their own droll way.

CHAPTER XV

THE MYSTERY CAVERN

Once their craft was repaired, the submarine party pushed northward at an average rate of ten miles an hour. It was two days before any further adventure crossed their path. But each hour of the journey had its new thrill and added charm. Now, with engine in full throb, they were scurrying along narrow channels of dark water, and now submerging for a sub-sea journey. Now, shadowy objects shot past them, and Dave uttered a prayer that they might not mix with the propeller--seal, walrus or white whale, whatever they might be. In his mind, at such times, he had visions of floating beneath the Arctic pack, powerless to go ahead or backward and as powerless to break through the ice to freedom.

Wonderful changing lights were ever filtering through ice and water to them, and, at times, as they drove slowly forward, the lights and shadows seemed to have a motion of their own, a restless shifting, like the play of sunlight and shadow beneath the trees. Dave knew this was no work of the imagination. He knew that the ice above them was the plaything of currents and winds; that great cakes, many yards wide and eight feet thick, were grinding and piling one upon another. Once more his brow wrinkled. "For," he said to himself, "it may be true enough that the average ice-floe is only twenty-five miles wide, but if the wind and current jams a lot of them together, what limit can there be to their extent? And if we were to find ourselves in the center of such a vast field of ice with oxygen exhausted, what chance would we have?"

Dave shuddered in answer to the question.

He was thinking of these things on the eve of the second day. They were plowing peacefully through the water when, of a sudden, there came a grating blow at the side of the craft. It was as if they had struck some solid object and glanced off.

"What was that?" exclaimed the boy. He cut the power, then turned to the Doctor:

"Ice or--"

"There it goes again!" exclaimed the Doctor.