Which was very good advice, first and last, and more than one boy in khaki had heard it.
“Do you know wherre we arre?” Archer asked.
“I know about where we are,” Slade answered. “Throw your searchlight over there. See that kind of black——”
“Yes, I see it,” Archer interrupted.
“I think that’s the hills near Barsaby,”[[5]] Tom replied. “Wait till I see what time it is. There’ll be a train leaving there about eleven, going down to Chatillon. It whistles just before it goes in the tunnel. If I hear that I can tell about where we are.”
“Maybe it can’t run,” Archer reminded him.
“It’s got to run—that’s a commissary centre,” Slade said. “And it’s right along the mountains anyway.” He looked at his watch and saw that it was fifteen minutes of eleven.
“What do you mean to do?” Archer asked, a bit puzzled.
“If I hear that whistle, I can tell just about where we are,” Slade said. “If it sounds kind of dim south of here I’ll know we’re just about east of Troyes. I know we’re east of Troyes but I can’t tell if we’re a little north or a little south of it. I’d rather use my ears than a compass a night like this. I can run her straight west all right, right into the wind, but if I’ve got to climb upstairs I want to know it.”
Archer did not fully understand, nor indeed did I, except I infer that Slade intended to measure the almost exact distance to a certain place (Bar-sur-Aube) by the whistle of a locomotive and to lay his aerial course accordingly. I think that here was another instance of the value of his woods lore and scout training.