Dave wiped the cold perspiration from his brow, as the hand on the dial dropped lower and lower.  He touched a wheel again, and they rose another ten feet.  “Must be nearly bumping the ice by now; but at such a time as this one takes risks,” he muttered.

What was that?  Did he sense the dark shadow which always presaged open water?  Surely, if walrus were about, there must be open water to give them air.  And, yes—­there it was; a hole in the floe!

His trembling hand again touched the wheel.  The hand on the dial had dropped to nearly nothing.  If the water-hole was narrow; if they missed it!

But no—­up—­up they shot, and in just another moment men were swarming from the conning-tower.

“Say!” exclaimed Dave, wiping his forehead.  “Do you remember the obstacle-races they used to have at county fairs when you were a boy?”

The jackie he spoke to grinned and nodded.

“Well, this is an obstacle-race, and the worst I ever saw.  The worst of it is, there are two prizes—­one’s the Pole and the other our own lives!”

The open water they had reached at so fortunate a moment proved to be a channel between floes.  They were in no immediate danger now, but to repair the damage done to the shaft and adjust a new propeller, it was necessary that they drag the submarine to the surface of a broad ice-cake.  This task was not as difficult as one might imagine.  With the aid of ice-anchors, iron pulleys and cables, they without much delay harnessed their engine and finished the job all ship shape.

“Look!” said one of the seamen, pointing at the narrow stretch of water.  “She’s closin’ in!”

As the men looked they knew it to be true; the channel was certainly narrower than when they first rose upon its surface.

Securing a light line, the Doctor attached it to a plummet.  Throwing the plummet across the space, he drew the line taut.  He then marked the point where the ice-line crossed it.  Then for five minutes he divided his attention between the line and his watch.  As he rose he muttered;

“Two hours!  Two hours!  How long will it take to complete the repairs?”

“Four hours, at least,” Dave replied calmly.

“Then we’re defeated!” The Doctor began pacing the surface of the ice.  “We’re stuck—­beaten!  In two hours the channel will be closed, and there is not another patch of open water within five miles!”

If Dave seemed unnaturally calm on receipt of such news, it was because he had in his “bag of tricks” one of which the Doctor was not aware.  While in Nome he had made the acquaintance of a former British seaman, who had cruised Arctic waters in the late eighties, when Japan was disputing the rights of Great Britain and the United States to close the seal fisheries.  This man had told him how the gunboats had opened their way through the ice-floes.  The idea had appealed to the young skipper.  Consequently, on boarding the submarine, he had carried under his arm a package which he handled very carefully, and finally deposited in the very center of a great bale of fur clothing.  There it still remained.