His glance widened and seemed to be following some disappearing object. Then he sat straight upright, stared fixedly down the hill, and leaning over pulled his companion by the sleeve. "Dave! Dave!" whispered the excited boy-"wake up! We've been discovered!" CHAPTER XXI A CHASE IN MID AIR Dave roused up, wide awake in an instant. He was about to spring to his feet, when Hiram pulled him back with the words: "Don't get up." "Why not?" inquired the somewhat puzzled young aviator. "You'll be seen." "Who by?" "A man who was just here." "Do you mean that, Hiram?" exclaimed Dave in a startled tone. "I certainly do. Look," said Hiram, pointing, and then he added: "No, the trees shut him out now. As I just said, though, we have been discovered." Now Hiram arose to his feet, the danger of being seen appearing to have passed. Dave followed his example. "Some one was here, you say?" began Dave. "Yes." "Who was it?" "A fellow who looked like some of the half breed Indians we saw fishing over near Anseton. I woke up, and he came in range clear as a picture. It was over by that thicket of pine trees. There he stood, staring at our machine, then at us. He seemed to take it in with a good deal of surprise. Finally he threw up his hands as if he was making up his mind to something, and started on a run down the hill." "In that direction?" asked Dave, pointing due east. "Yes, in the direction of Brantford. I tell you, Dave, he's a spy. If he ran across us accidentally then he's gone to tell his friends about discovering the airship." "That doesn't follow," remarked Dave thoughtfully, "but I'm glad you saw him." "Yes, I think we need to keep a pretty close lookout. Say, Dave," questioned Hiram, "if he is some friend of the Dawson crowd, and has gone to tell them about us, what do you suppose they'll do?" "I have no idea," replied the young aviator. "But they won't catch us napping." Dave kept a close watch out in all directions while Hiram hurried up a quick breakfast. They got through with the meal rapidly. Then Dave went over the machine, seeing that the gasoline tanks were full and the gearing and oiling apparatus in good order. Two hours went by, and there were no developments that indicated that the visitor to their camp had been other than a straggler, with no purpose in view in his rapid disappearance. Hiram became more matter-of-fact, and guessed he had "got scared for nothing." All the same he kept a close lookout all of the time, particularly in the direction of Brantford. Dave was planning a visit on foot to that town. He decided, however, that he would wait till afternoon so as to be sure that there was no occasion for worry. Both lads discovered the fallacy of their theories at the same moment. "Look!" suddenly shouted Hiram, pointing. "I see," said Dave calmly, but under the surface greatly stirred up. "It's the Drifter!" "Yes." "What are you going to do?"