"Wait," said one German. "I've some gasoline."
Rapidly he opened up a big can, which he took from the bottom of his machine. Quickly the tank was filled and the man climbed into the pilot's seat. Another jumped in with him.
"Give us some of that gasoline!" cried another.
The German shook his head.
"Not enough," he replied. "We'll overtake those fellows and then come back for the rest of you."
The aeroplane leaped skyward and started in pursuit of Frank and Jack.
The two boys, believing that they were safe, were going along only at a fair rate of speed when Jack's keen ears caught the sound of the pursuing machine.
"They're after us, Frank!" he called.
"Impossible!" replied Frank. "How can they fly without gas?"
"Well, they're coming, all the same," declared Jack.