He drove these thoughts from his mind. The passage had to be made on the fickle authority of the senses; and, realizing this, Wells took the helm into his own hands. Graham was posted at the location chart, with instructions to report the red light if it showed. * * * * * Down below, the Edsel electrics were humming very softly; the men stood vigilantly at posts. On their brows were little beads of sweat, and here and there a hand clenched nervously. All knew they were in a tight place; otherwise they were ignorant of where their commander was leading them. Occasionally a long, shivering rasp ran through the ship as her hull nudged the rough tunnel wall. Then the course rudders would swing gently over; and perhaps, almost immediately, another grinding cry of rock and steel would come from the other side. Then would come quickly indrawn breaths as the rudders swung again and the humming silence droned on. The scrapings came quite often. Often, too, the motors would go silent altogether, and the _NX-1_ would rest almost motionless as her commander felt for an opening. It was a tense, nerve-wringing ordeal. The silence, the waiting, the dainty scrapings were maddening. Keith Wells' skin was prickling. He kept only fingertips on the tiny helm: he was playing that uncanny sixth sense of the submarine commander. When it misled him, the rasping rock groaned out, scarring the submarine's smooth skin. Generally, the tunnel was straight; but each time he heard his ship rub against some exterior obstruction, his teeth went tight--for who knew but what it might be a mine? They had penetrated perhaps a half-mile when Graham, eyes steady on the teleview, reported: "Light growing, sir!" * * * * * Wells saw that the screen was filling with a soft, faintly glowing bluish color. The walls of the tunnel became visible, and he noted that they were widening out, funnel-like. He dared to increase speed slightly. Three minutes later he saw that the blue illumination was seeping from the end of the tunnel. They continued out. "Thank God, we're through!" he muttered to Graham. "You see, I was right! It's an underground sea--and we're at the top of it." For the instruments indicated a depth beneath them of roughly three miles. They were in, evidently, a large cavern, of vast length and depth. The _NX-1_ continued slowly forward, two pairs of eyes intent on her teleview screen. Keith jotted down the tunnel's position, and the funnel-shaped hole sank away behind their slow screws. And then, upon the location chart, a faint red dot suddenly glowed! It was upon them in a flash. A small tube of metal, shaped somewhat in the form of the big octopi submarine, had darted up from below, hovered a second close to them, and then, almost before they realized they were being surveyed, sped back into the mysterious depths from which it had come.