"I thought so!" he said, with suppressed triumph in his voice. "Do you see those barrels over there toward the inn? There's petrol in those—or I'll eat my shirt!"

"And if there is?" said Henri. "What then?"

"Can't you guess? What do you suppose those lights mean?"

"Aeroplanes?"

"Never! They wouldn't flash that way. They'd have to be in a different position entirely. No. Dirigibles!"

"Zeppelins?"

"Perhaps. Perhaps Parsevals or Schutte-Lanz airships. I think Parsevals, for they need gasoline. And Zeppelins could fly from Brussels or Liege, almost from Cologne—oh, I have it! That's why they need petrol!"

"Why?"

"They haven't flown over Belgium at all! They are from the sea!"

"Oh—so that they could come secretly, and not be seen as they passed over Belgium?"