Dr. Giles heard this rumbling too, and the whole truth flashed upon him in an instant. Something must have happened to the tube! The devices for converting the heat into electricity must in some way have become injured, and now refused to work properly.
The doctor's face blanched as he realized the full meaning of these signs.
Evidently, if the apparatus was out of order, the internal heat of the earth, having no longer a free outlet, would rapidly accumulate, producing such a temperature that the tube would melt; and what would then become of the brave boy who had dared this unknown danger for the sake of his mother?
With set faces, our three friends watched the instruments, when suddenly they were startled by a loud report like distant thunder, accompanied by a shock that set the whole office vibrating. Dr. Giles cast one agonized look at the instruments, and then fell back in his chair.
"William is lost!" he cried in anguish. "The carbonite tube has given way. The poor boy's death is certain; for I am absolutely powerless here, and can only stand idly by and let matters take their course!"
