"Have you any extra cartridges?" she asked.
"Not a single one, but the revolver itself is fully loaded. That's just six we have to count on."
She was silent for a moment.
"There isn't any likelihood we'll have to use these for defending ourselves," she said at length. "There doesn't seem to be any living thing in this cave of which we need to be afraid. But, nevertheless, suppose we keep two for emergencies. That would give us four to experiment with, wouldn't it?"
"Experiment? How?" he inquired.
"I was thinking that perhaps father"—here her voice faltered a little—"and Tyke might be somewhere in the neighborhood hunting for us. If we should discharge the revolver they might possibly hear one or more of the shots and get some idea of where we were. I know it's only a forlorn hope, but we've got to try everything just now."
"It's a good idea!" exclaimed Drew, though he knew in his heart how slender a chance it offered. "And in the meantime, I'll keep on digging, so that if the shots aren't heard we won't be any worse off anyway. You fire the four shots at intervals of a minute or two and we'll see what happens."
He went savagely to work again and Ruth at short intervals discharged the revolver. The noise and the echoes in that compressed space were deafening and it certainly seemed as though the sound ought to penetrate to the world outside.
But though they fairly held their breath as they listened for a response, no answering sound penetrated from the outside into the cavern, and their hearts sank as they realized that one more of their few hopes had failed them.
"It's of no use," observed Ruth sadly, as she handed the weapon back to Allen. "Either they didn't hear the shots, or, if they did, they thought it was some sound made by the volcano. We'll have to try something else."