Taking a letter from his pocket, Dick bored a tiny hole in it with his scarf pin. Through this hole he found he could see in comparative comfort. He signed to the others to do the same, and soon all four—for Yvette quickly recovered her self-possession—were eagerly watching the strange scene before them. Speech, in the deafening noise by which they were surrounded, was, of course, out of the question.
The man at the great table in the centre of the cavern evidently had a task of great difficulty to control the movements of the strange machine, which he seemed to do by means of a large wheel something like the steering wheel of a steamer. Long streamers of flame shot from it in all directions, and as its mass of wheels revolved at terrific speed it shook and trembled as if it would actually leap from the table.
In the meantime the men at the rock face were hard at work with big blowpipes, from the muzzles of which shot streams of fire of such intensity that the solid rock seemed to melt away like butter. The molten matter was led by ducts in the ground through a grid of some metal, evidently highly refractory to heat, for it appeared to do no more than glow white-hot even in the terrific temperature of the melted rock. After passing through this grid the molten matter was led to the bed of the stream, from which the water had in some manner been cut off, and flowed out the way Dick and his companions had entered.
What was the object of the work?
Dick could not guess, but every now and again one of the men would walk to the grid and with a long implement shaped like a hoe would scrape off something adhering to the bars, which he deposited in a big tank of water. Dick determined that, sooner or later, he would obtain a specimen.
But in the meantime their position was decidedly precarious. If they were observed there was no possible way of escape, for the tunnel by which they had entered was barred by the stream of molten matter. They could only lie still and hope that no one would enter the gallery in which they lay concealed.
After two hours of work, the man at the table stopped the machine, and all the men straightened out for a rest. Evidently they were very much exhausted. The lights were extinguished, except for the single one which was burning when they entered, and the men returned to their quarters, evidently almost falling with weariness. Dick came to the conclusion that they could only carry on the work on which they were engaged for a short time and that after that sleep and rest were imperative. The flow of molten metal had stopped and the water was again allowed to flow along its ordinary channel, from whence it sent up huge clouds of dense steam.
This gave Dick his chance.
Sending the others to the mouth of the exit, he cautiously crept towards the tank in which were deposited the scrapings from the grid which filtered the molten rock. He reached it safely, and plunging in his arm up to the shoulder, abstracted a couple of handfuls of what seemed like heavy shot. These he placed at once in his pocket.
He was about to return to the others when his attention was caught by the queer platform at the one end of the cave. Looking at this carefully he found that it was really a huge lift, and at once the mysterious disappearance of the sailor and the mules was explained. It was evident that the top of the lift was really the thin covering of rock which had sounded hollow when tapped and that this had been so cut that when the lift forced it into position only traces of ragged crevices were left on the surface. Dick could not but admire the ingenuity with which this approach to the subterranean retreat had been devised.