“Yes, that’s true enough,” replied Dick. “But just at present I don’t want to be put out of business over night if I can help it. Every aviator on this sector is on the lookout for a certain Boche plane that has been making a pest of itself around here, and the one that succeeds in bringing him down is going to be considered a real ace.” “Why, has he been doing such a lot of damage?” asked Billy. “Damage!” exclaimed Dick, “I should say he has been doing damage. And not only that, but he does it in such a way that none of us so far has had any chance for a comeback.” “How’s that?” inquired Tom. “His favorite stunt is to come over our lines along about dusk, and drop his load of bombs where he thinks they will do the most good. Then he makes a quick turn about and escapes, either going directly back to his lines, or, more often, rising high enough to reach a cloud stratum, and hiding in that. And by the time our fellows get out after him, it’s so dark that there’s no chance of seeing him. He’s responsible for the death of any number of our fellows, and nobody knows how much damage to roads and ammunition trains.” “That’s the Boche’s regular game,” commented Frank, bitterly, “their ’planes always run the minute they think a superior force is coming out against them. It would be wonderful if you could be the one to capture him, Dick.” “Wonderful! I should say it would,” exclaimed the young aviator. “But that tricky way he has of cloud hiding, together with his habit of only attacking right on the edge of darkness, makes it a mighty hard proposition to come up with him. But I or one of the other fellows will get him eventually, never fear.” “If only there were some way to tag him so that he could be followed easier,” said Frank, slowly. “Yes, but that’s a pretty big if,” said Billy, “supposing you come down to earth and give us some practical suggestion about how it’s going to be done.” “Well, maybe I will,” replied Frank, to whom had come the glimmering of an idea, “you fellows know that illuminating paint they use for signs, and so forth, so that they can be read in the dark, don’t you?” “Right you are!” exclaimed Dick, who grasped the other’s thought in the twinkling of an eye, “if we could douse this Boche’s plane with some of that mixture, a blind man could follow his progress after dark. But then,” he concluded, less enthusiastically, “the problem arises as to how we are going to get the paint on his machine. It reminds me of trying to catch a bird by putting salt on his tail.” “Well, it might be worth trying, anyway,” said Frank, defending his project. “Why couldn’t you take a pail of this with you, and then there’s a bare possibility that you might be able to drop some of it on him. One splash of that stuff on his machine, and you’d have the easiest job in the world following him. The darker the night, the better.”