The back yard of the McReady home stretched down to the cottonwoods that fringed the bank of the canal. Here, in an old poultry-house, Mark, otherwise "Chub" McReady, did most of his experimenting. A dozen feet from the "laboratory" was a tall pole rising some forty feet from the ground and overtopping the trees. At its lofty extremity was an arm with the tip of a lightning-rod swinging downward from its outer end. "How's the wireless working, Susie?" asked Matt as they moved toward the canal. "Mark got a spark from the Bluebell Mine last night," said Susie; "just one flash, that's all. After that something seemed to go wrong. That's generally the way with Mark's inventions, Matt. I wish he'd stop fooling away his time; but, even if his time isn't valuable, there's always the expense. Welcome encourages him, though, and furnishes most of the money. I wonder where Welcome gets it?" "Welcome's a sly old possum in spite of his foolishness, and it's my opinion he's got a stake settled away somewhere. This wireless-telegraph experimenting is harmless enough, but I'm Dutch if I think it's the right thing for Chub to tamper with this smokeless-powder idea. Something might happen, and----" Just then something _did_ happen, something that was clearly not down on the program. There was a muffled roar from the laboratory, followed by a burst of smoke from the door and the open window. With a wild yell, Welcome Perkins rolled through the window, heels--or heel--over head. He was on fire in several places. A chunky, red-haired boy came through the door as though he had been shot out of a cannon. This was Chub, and he was badly singed. "Whoo!" yelled Chub, coming to a dazed halt and rubbing one hand across his eyes. "That was a corker, though. I guess something went crossways. Say, Perk! Hold up there, Perk!" Welcome Perkins had scrambled erect and was stumping along for the canal like a human meteor. He was carrying his hat and seemed to think his life depended on getting where he was going in the shortest possible time. Without waiting to explain matters to Matt and Susie, Chub darted after Welcome. "Goodness' sakes," screamed Susie, "the laboratory is burning up!" "Small loss if it does burn up," answered Matt, "but we'd better do what we can to put out the fire and keep sparks away from the house." Matt ran swiftly into the kitchen of the adobe house, picked up a bucket of water and darted back toward the laboratory. There was a good deal of smoke, but not very much fire, and the single pail of water was enough to quench the flames. But the interior of the laboratory was completely wrecked. "There'll be no conflagration, Susie," announced Matt, coming out of the place and joining the girl near the door. "Chub was a lucky boy to get out of that mess as well as he did. Let's hike for the canal and see what he and Welcome are doing."