"It's a heat-engine, you know--works by absorbing heat. The cold air sinks--I imagine it pretty nearly blows a gale down the side of this cone when it's working--and hot air rushes in to take its place. I could use a little cool breeze right now," and Stevens, stripped to the waist, bent to the lever of the powerful hydraulic jack. Beads of sweat gathered upon his broad back, uniting to form tiny rivulets, and the girl became highly concerned about him. "Let me help you, Steve--I'm pretty husky, too, you know." "Sure you are, ace, but this is a job for a truck-horse, not a tenderly-nurtured maiden of the upper classes. You can help, though, by breaking out that welding outfit and getting it ready while I'm doing this bending to prepare for the welding." Under the urge of that mighty jack the ends of the broken bus-bar rose into place, while far off in space the Titanians clustered about their visiray screens, watching, in almost unbelieving amazement, the supernatural being who labored in that reeking inferno of heat and poisonous vapor--who labored almost naked and entirely unprotected, refreshing himself from time to time with drafts of molten water! "All x, Barkovis--that's high, I guess." Stevens flipped perspiration from his hot forehead with a wet finger and straightened his weary back. "Now you can put this jack away where we had it. Then you might trundle me over enough of that spare metal to fill up this hole, and I'll put on my suit and goggles and practice welding on this floor and the roof, to get the feel of the metal before I tackle the bar." The hole in the floor was filled with scrap and soon sparks were flying wildly as the searing beam of Stevens' welding projector bit viciously into the stubborn alloy of noble metals; fashioning a smooth, solid floor where the yawning aperture had been. Then, lifted with his tools and plates to the roof, the man repaired that hole also. "Now I know enough about it to do a good job on the bar," he decided, and brick after brick of alloy was fused into the crack, until only a smoothly rounded bulge betrayed that a break had ever existed in that mighty rod of metal. "Give 'em the signal to draw power, and see if that's all that was the matter," Stevens instructed, as he relaxed in the grateful coolness of their control room. "Whew, that was a warm job, Nadia--and this air of ours does smell good!" * * * * * "It was a horrible job, and I'm glad it's done," she declared. "But say, Steve, that thing looks as little like a power-plant as anything I can imagine. How does it work? You said that it worked on heat, but I don't quite see how. But don't draw diagrams and _please_ don't integrate!"