He couldn't understand what had happened to him. He pulled his right arm inside the suit with an effort and probed the painful area on his chest. He felt the hot wetness of flowing blood. He would have to get to the sphere. He tried to move. He couldn't get off his back. He lay there and writhed in pain. Jonner's voice was in his ears, saying something. "I knew it would get you," Jonner said. "It was my only chance. But it got you at last, Kraag." "Come help me, Jonner," whimpered Kraag weakly. "I've been hit by ... I don't know. It must have been a meteor." "I'm coming as fast as I can, Kraag, but it was no meteor. It was my gun." "Gun?" repeated Kraag wonderingly. "I warned you about that gun of mine, Kraag. If you'd looked at the figures on the barrel, the muzzle velocity of those .45-calibre bullets is 1100 feet a second. With Ceres' escape velocity, that's almost exactly the circular velocity at the asteroid's surface." Jonner was standing over him, and then was lifting him gently, to carry him to the sphere. "I deliberately got just out of your range of vision, from the ground, so you'd climb to a high spot," said Jonner. "You had to be high, so the bullet would clear the irregularities on the planet's surface, and I knew that sooner or later you'd shoot a bullet or two high enough not to hit the ground. "When you were firing at me, your bullets weren't describing a trajectory and falling to the surface, as they would on Earth or Mars. They were taking an orbit that brought them all the way around the planet to the same spot, to hit you from the other side two hours later." Kraag tried to look up at him. Something was going wrong with his sight, and everything outside his face plate was a blur. Must be the oxygen ... maybe his suit didn't seal the bullet hole properly. "I thought...." Kraag began, and choked. He coughed, slowly and painfully, then tried again: "I thought that ... problem on the rocks ... looked familiar." "You've always done it with a slide rule. That's probably why the long division didn't register," said Jonner. "The equation is one every spaceman knows: the circular velocity equals the escape velocity divided by the square root of two."