“Can this have anything to do with it?” suggested Wilmot, offering a charred bit of wood which he had picked up from the floor. The instructor took it, smelled of it, and shook his head. “I don’t know,” he said. “If these explosions are due to the sand, it is a remarkable occurrence. If they were deliberately caused, it is a very dangerous and culpable form of joke. We shall take only one experiment to-day. As soon as you have finished with that, you may go.” Mr. Cary stood close to Wilmot’s desk during the rest of the exercise, either because it was in a central position or because he saw in the disturbance the fine Italian hand of that young gentleman. One awkward result for Wilmot was that, not daring to take the match-box from his drawer in the presence of the teacher, he was obliged to leave it behind when he went. Dunn, too, made a misplay. He had used two of the three matches taken from Wilmot’s box on Redfield and Dobbs; not knowing what to do with the third, he broke off the end and poked it into the bag of fresh sand which stood at the end of his table. The first thing Mr. Cary did after the boys had left the laboratory was to examine the sand in the bag. At the very top, like Benjamin’s cup hidden in the mouth of the sack, he found the match-end which Dunn had placed there. He compared this with the charred piece picked up by Wilmot. Over these he mused a few minutes; then, with the instinct which sends the police, after an important break, to the haunts of certain well-known criminals, he went straight to Wilmot’s drawer. There, under the soiled laboratory coat, he discovered the fatal box. He broke off a match-head, put it into a sand bath, and in five minutes had an explosion of his own. After that he gathered up his exhibits and hied him to Mr. Westcott’s office. The laboratory excitement furnished a topic of deep interest to certain groups during the lunch hour. Dunn, who was sure that he had made a hit, talked largely of his achievement. Wilmot, though pleased with the unexpectedly full success of his idea, was a little worried that he had been forced to leave his treasure in the laboratory. It wouldn’t do to use the thing too often, and Dunn was capable of firing off all the precious matches in a day. By the end of recess, largely through Dunn’s enthusiastic narratives, the incident had been aired among the older boys. Towards two o’clock word came to Wilmot that he was wanted in the head-master’s office.