"About a quarter of a mile behind us, I should judge!"
"After a bit we'll make it a whole mile," smiled Ned.
At that instant the boys heard a peculiar whizzing noise. It was followed by a sharp report from the rear. A puff of white smoke showed from the pursuing machine, but quickly disappeared.
"He's shooting at something!" declared Jack.
Ned glanced at his companions. Again the peculiar noise was heard, followed by another report and another cloud of smoke.
"Great Frozen Hot Boxes!" cried Jimmie. "He's shooting at us!"
CHAPTER VIII. Imperiled in a Trap.
"He can't be shooting at us!" protested Harry vigorously. "We haven't done anything to him. It must be a mistake!"