They swooped low over the dark surface, taking observations and measurements. "It's not as cold as we might suppose," said Oberfield after his first readings. "There's a certain amount of heat all along the rim of the dark side. Radiation, I suppose, as well as the fact that there's a certain amount of wobbling done by the planet." Burl was studying the surface. "Seems to me that much of the dark side has a gleam to it. Something reflects the stars; I see little glints of light, shifting and blinking." "I can guess what that is," said Russ. "It must be covered, at least in the central portions, with a sea of frozen gases. What atmosphere Mercury had long ago must have congealed there." The ship moved along toward the twilight edge, then began circling the planet along that intermediate belt, where the Sun could be seen peeking over the horizon in eternal dawn. There was a cluster of men at the radiation counter, looking for evidence of the Sun-tap station. Finally, after passing over a chain of darkened mountains, eerily lighted at the peaks by the Sun, there came a yell. Distortion had been detected. Once on it, they swung the ship outward into space again and moved along further over the sunlit side. Burl stared into the telescopic viewers as they probed the surface. He saw an ugly and terrifying world. The planet, which had a diameter of only 3,100 miles, compared to Earth's 7,900, was virtually without an atmosphere. Its surface was baked hard, brilliantly white, covered with long, deep cracks that cut hundreds of miles into the shriveled and burned surface. There were areas of dark mountain ranges, bare and jagged, whose metallic surfaces imparted a darker shade to the pervading glare. And there were patches here and there on the surface that gleamed balefully--probably spots of molten material. Haines, standing next to him, was muttering, "It can't be too far in, it can't. How could they build it?" Then Burl found what they were looking for. A huge canyon tore raggedly across a plain. There was a jumble of mountains, a chain edging in from the twilight zone. And in a corner, about two hundred miles out into the hot side, at a narrow ledge where the mountains came down and the canyon came together, there was a circular structure. They could see, as soon as the telescopic sight had been adjusted, that it was a large station. It was encircled by a featureless wall. It had no roof. Rising on masts above it was a whole forest of gleaming discs pointing at the Sun low in the sky. On the tops of the mountain peaks, a half mile from the station, was another series of masts. These were aimed away from the Sun into the dark airless sky and toward the other planets. "The accumulators and the transmitters," said Burl. "We'll have to get them both." "Getting the transmitters will be easy," said Haines. "After we shut off the station, we'll just bomb the mountain masts out of action."