No answer being made to his inquiry, he gripped his gun more firmly and crawled cautiously toward the spot where he thought he had heard some one moving. The night was so dark that he could make nothing out of the shadows about him, being obliged therefore to trust entirely to his sense of hearing.
Now he was certain that some one was in camp who had no business there, for the sound of footsteps was plainly borne to his ears—cautious, catlike steps, as if the intruder were seeking to get away without attracting attention.
The Professor, determined to capture the intruder, getting down on all fours to avoid possible detection, made a wide detour so as to come up behind where the fellow seemed to be at that moment. After much labor he managed to reach the desired position.
The Professor straightened up to listen. He must be close upon the other by this time. But what was his chagrin to hear those same footsteps on the opposite side of the camp. Professor Zepplin by much effort had just come from the other side himself.
"Stupid!" he muttered. "I'll take no roundabout way this time. I'll go straight ahead and be as quiet about it as I can."
He did so. He moved straight across the camp ground, not forgetting the saddle which he carefully avoided, but narrowly missing falling over it a second time.
By the time he had crossed to his former position, the intruder had done likewise. Professor Zepplin dodged behind a tree.
By this time the scientist was beginning to feel a little worried. He could not understand what the other fellow's object might be. If it were robbery, the fellow certainly would desire to get away as quickly as possible, rather than remain when he knew that efforts were being made to capture him. If not plunder, what could be his purpose?
With suddenly formed determination, Professor Zepplin strode out from his hiding place, starting for the other side on a run.
The other man did the same, and the only result of the move was that their positions were exchanged.