The workmen returned with two smaller cases; one of each they placed on benches to either side of the big tube. They knocked the boxes apart and there emerged two smaller editions of the center tube--and even Arden could see that these two were quite like the forward half and the latter half, respectively, of the larger tube. "Did you buy 'em out?" she asked. "No," said Don simply. "This merely makes a complete circuit." "Explain that one, please." "Sure. This one on the left is the input-terminal tube which they call the power-end. The good old D. C. goes in across these two terminals. It emerges from the big end, here, and bats across in a beam of intangible something-or-other until it gets to the relay tube where it is once more tossed across to the load-end tube. The power is taken from these terminals on the back end of the load-end tube and is then suitable for running motors, refrigerators, and so on. The total line-loss is slightly more than the old-fashioned transmission line. The cathode-dynode requires replacement about once a year. The advantages over high-tension wires are many; in spite of the slightly higher line-losses and the replacement trick, they are replacing long-lines everywhere. "When they're properly aligned, they will scat right through a mountain of solid iron without attenuation. It takes one tower every hundred and seventy miles, and the only restriction on tower height is that the tube must be above ground by ten to one the distance that could be flashed over under high intensity ultraviolet light." "That isn't clear to me." "Well, high-tension juice will flash over better under ultraviolet illumination. The tube must be high enough to exceed this distance by ten to one at the operating voltage of the stuff down the line. Another thing, the darned beam can be made to curve by adjusting the beam plates in the tube. The boys in the Palanortis Jungles say they're a godsend, since there are a lot of places where the high-tension towers would be impossible since the Palanortis Whitewood grows about a thousand feet tall." "You'd cut a lot of wood to ream a path through from Northern Landing to the power station on the Boiling River," said Arden. "Yeah," drawled Don, "and towers a couple of hundred miles apart are better than two thousand feet. Yeah, these things are the nuts for getting power shipped across country." "Couldn't we squirt it out from Terra?" asked Arden. "That would take the curse off of our operating expenses."