"And that was done because of an emergency. Probably this other thing will go on until we hit an emergency; then we shall prove that old statement about a loaf of bread being the maternal parent of a locomotive." Channing lit a cigarette and puffed deeply. "Where do we stand?" "Thirty hours out," answered the steward. "About ready for turnover. I imagine that the power engineer's gang is changing cathodes about now." "It's a long drag," said Channing. He addressed himself to his glass and began to think of a suitable answer for his wife's latest thrust. Bill Hadley, of the power engineer's gang, spoke to the pilot's greenhouse below the ship. "Hadley to the pilot room; cathodes 1 and 3 ready." "Pilot Greenland to Engineer Hadley: Power fade-over from even to odd now under way. Tubes 2 and 4 now dead; load on 1 and 3. You may enter 2 and 4." "Check!" Hadley cracked an air valve beside a circular air door. The hiss of entering air crescendoed and died, and then Hadley cracked the door that opened in upon the huge driver tube. With casual disregard for the annular electrodes that would fill the tube with sudden death if the pilot sent the driving power surging into the electrodes, Hadley climbed to the top of the tube and used a spanner to remove four huge bolts. A handy differential pulley permitted him to lower the near-exhausted cathode from the girders to the air door, where it was hauled to the deck. A fresh cathode was slung to the pulley and hoisted to place. Hadley bolted it tight and clambered back into the ship. He closed the air door and the valve, and then opened the valve that led from the tube to outer space. The tube evacuated and Hadley spoke once more to the pilot room. "Hadley to Greenland: Tube 4 ready." "Check." The operation was repeated on tube 2, and then Pilot Greenland said: "Fade-back beginning. Power diminishing on 1 and 3, increasing on 2 and 4. Power equalized, acceleration two G as before. Deviation from norm: two-tenths G." Hadley grinned at the crew. "You'd think Greenland did all that himself, the way he talks. If it weren't for autopilots, we'd have been all over the sky." Tom Bennington laughed. He was an old-timer, and he said in a reminiscent tone: "I remember when we did that on manual. There were as many cases of _mal-de-void_ during cathode change as during turnover. Autopilots are the nuts--look! We're about to swing right now, and I'll bet a fiver that the folks below won't know a thing about it." * * * * * A coincidence of mammoth proportions occurred at precisely that instant. It was a probability that made the chance of drawing a royal flush look like the chances of tomorrow coming on time. It was, in fact, one of those things that they said couldn't possibly happen, which went to prove only how wrong they were. It hadn't happened yet and probably wouldn't happen again for a million million years, but it did happen once.