"Now," said the Doctor, "start the power slowly, engine reversed. The instant she is free, shut off the power. On the precision of this operation depends all our lives, for should the propeller strike one of those pillars it will be torn away and our hope of escape gone."
Dave's hand trembled as he moved the lever. For one second the propeller spun around. Then, with a shudder, the craft started backward. That instant Dave shut off the power. The submarine drifted free. So far, they were safe.
The Doctor consulted his watch.
"Time of low tide," he observed "Guess we should be able to rise and get some air. Try it."
Slowly they rose to the surface, and there the craft rested.
It was an eager throng that rushed from the conning-tower and it was a wonderful and awe-inspiring sight which met their gaze.
"Cathedral of the Polar Gods!" exclaimed the Doctor. And, indeed, so the great cavern seemed to be. Great pillars of ice, not yet worn away by the wash of water, supported giant arches of ice, blue as a mid-June night. The least echo was echoed and reechoed through the vast corridors. The murmur of distant waves seemed to come from everywhere.
"What I want to know," said Dave, "is, which way is out. The careless gods seemed to have neglected to mark the exits."
"We'll find an exit," said the Doctor, "and we'd better be about it, for it'll be much easier at low-tide than at high."
The engine was started, and slowly they steered their way through countless aisles and broad halls, but the finding of the way out did not seem so easy after all. They had penetrated far enough into the cavern to hide them from the pale outer moonlight, and they were not certain that their course was not taking them farther from it.