“By Jove, it’s worth trying, anyway,” said Dick, caught up on a wave of enthusiasm. “I’ll try anything once, anyway. But now the question is, where are we going to get the paint?” “There’s a supply wagon not over a mile from here,” replied Frank, “if you’re game for the hike, I’ll go with you, and we’ll see if we can’t get some.” “You’re on!” exclaimed the aviator. “You two fellows stay here to see that no one monkeys with my machine,” addressing Billy Waldon and Tom Bradford. “All right,” agreed Tom. “But you’d better shake a foot or some of this bunch will be taking your machine apart for souvenirs,” and he laughingly indicated the interested group of doughboys who had by this time sauntered up. Frank and Dick set off at a smart pace, as they were all eagerness to try the novel experiment, and there was no time to lose, if it were to be done that night, as it was then after five o’clock, and nearing the time at which the German aviator usually made his raids. They maintained a brisk pace, and it was not long before they reached a group of supply wagons, carrying all sorts of supplies and equipment. They had some difficulty in explaining matters to the officer in charge, but at last he was moved by their enthusiasm, and gave them permission to draw a small pail full of the illuminating paint. This was a special mixture of chemicals, and was extensively used by our army for signs, indicating arrows, etc., where it was impossible or inconvenient to have a special light to show up the object at night. The two friends made short work of the return trip, and surprised those waiting for them by the promptitude of their return. “Gosh!” exclaimed Billy, “I can see the finish of that Boche already, when two speed merchants like you go romping on his trail. He’s got about as much chance as a cootie in a disinfecting tank.” “We haven’t got much time to spare,” said Dick; “it’s getting dark already, and I’ve still got to clean the spark plugs in my machine.” “We’ll all help you do that,” volunteered Tom, and with wrenches that Dick gave them, they soon had the offending spark plugs apart, thoroughly cleaned, and restored to their proper sphere of usefulness. Then, while some of the onlooking soldiers held the plane, Dick gave the propeller a whirl, and the motor started with a reassuring roar. “That sounds good,” said Dick, as he climbed into the pilot’s seat. “Now, hand me up that paint, and I’m off on the trail of the Hun.” Billy handed him the pail, and Dick, after carefully depositing it at his feet, waved his hand in farewell. The boys had just started a cheer for him, when they were interrupted by the sound of a heavy detonation. For a brief space the artillery of both sides had been silent, and they could tell from the sound of the explosion that it was not caused by a gun. Even as they all listened, it came again,--a dull, heavy shock that caused the very earth to shake, and this time it seemed nearer.