This acknowledgment is necessary if I am to say thanks to some experts to whom I am indebted. There is Captain Charles Benjamin, who read over the aviation parts of this book with pursed lips and a belligerent attitude toward questionable statements of fact or observation. There is Dr. John Drury Clark, whose authoritative knowledge of rocket fuels was the basis for admitted but not extravagant extrapolation on my part. There is the crew of a four-engined transport ship, who argued over my manuscript and settled the argument by a zestful, full-scale crash-landing drill--repeat, "drill"--expressly to make sure I had described all the procedure just right. There is Willy Ley, whom I would like to exempt from responsibility for any statement in the book, while I acknowledge the value of personal talks with him and the pleasure anybody who has ever read his books will recognize. And there is Dr. Hugh S. Rice of the Hayden Planetarium, who will probably be surprised to find that I feel I owe him gratitude. They are in great part responsible for the factual matter in this book. I think I may add, though, that I worked on it too. MURRAY LEINSTER "Ardudwy" Gloucester, Va. _Space Platform_ 1 There wasn't anything underneath but clouds, and there wasn't anything overhead but sky. Joe Kenmore looked out the plane window past the co-pilot's shoulder. He stared ahead to where the sky and cloud bank joined--it was many miles away--and tried to picture the job before him. Back in the cargo space of the plane there were four big crates. They contained the pilot gyros for the most important object then being built on Earth, and it wouldn't work properly without them. It was Joe's job to take that highly specialized, magnificently precise machinery to its destination, help to install it, and see to its checking after it was installed. He felt uneasy. Of course the pilot and co-pilot--the only two other people on the transport plane--knew their stuff. Every imaginable precaution would be taken to make sure that a critically essential device like the pilot gyro assembly would get safely where it belonged. It would be--it was being--treated as if it were a crate of eggs instead of massive metal, smoothed and polished and lapped to a precision practically unheard of. But just the same Joe was worried. He'd seen the pilot gyro assembly made. He'd helped on it. He knew how many times a thousandth of an inch had been split in machining its bearings, and the breath-weight balance of its moving parts. He'd have liked to be back in the cargo compartment with it, but only the pilot's cabin was pressurized, and the ship was at eighteen thousand feet, flying west by south.