All listened. There came a faint report, like that of a gun.
"It's the professor, Washington, and the two farmers searching for us!" exclaimed Mark. "They are firing their rifles."
"That's it! They can't find us because we are down in this hole," said
Andy. "If I only had a cartridge now I could give an answer."
There came another report. This time there was no doubt that signal guns were being fired, for the shot sounded quite close.
Jack put his hand in his pocket. His fingers touched something.
"Hurrah!" he cried. "I have my revolver and there are four shots left!"
He passed it over to Andy, who shot twice at intervals of about a quarter of a minute.
"Where are you?" they heard a faint voice calling from somewhere above their heads.
In reply Andy fired the last shot. It was responded to, and then, a few seconds later, a dark object loomed up at the opening at the top of the inclined plane. The prisoners, looking up, recognized the professor.
"Hello, down there!" he shouted.