--therefore, permit no unauthorized persons to go through this door. The machinery in the next room is your protection against the rigors of space. A thousand years from now, journey's end, you may have discarded it for something better--who knows? But if you have not, then here is your protection. As nearly as possible, this ship is a perfect, self-sustaining world. It is more than that: it is human-sustaining as well. Try to hurt yourself and the ship will not permit it--within limits, of course. But you can damage the ship, and to avoid any possibility of that, no unauthorized persons are to be permitted through this door-- Rikud gave the voice up as hopeless. There were too many confusing words. What in the world was an unauthorized person? More interesting than that, however, was the second door. Would it lead to another voice? Rikud hoped that it wouldn't. When he opened the door a strange new noise filled his ears, a gentle humming, punctuated by a _throb-throb-throb_ which sounded not unlike the booming of the engines last week, except that this new sound didn't blast nearly so loudly against his eardrums. And what met Rikud's eyes--he blinked and looked again, but it was still there--cogs and gears and wheels and nameless things all strange and beautiful because they shone with a luster unfamiliar to him. "Odd," Rikud said aloud. Then he thought, "Now there's a good word, but no one quite seems to know its meaning." Odder still was the third door. Rikud suddenly thought there might exist an endless succession of them, especially when the third one opened on a bare tunnel which led to yet another door. Only this one was different. In it Rikud saw the viewport. But how? The viewport stood on the other end of the world. It did seem smaller, and, although it looked out on the garden, Rikud sensed that the topography was different. Then the garden extended even farther than he had thought. It was endless, extending all the way to a ridge of mounds way off in the distance. And this door one could walk through, into the garden. Rikud put his hand on the door, all the while watching the garden through the new viewport. He began to turn the handle. Then he trembled. What would he do out in the garden? He couldn't go alone. He'd die of the strangeness. It was a silly thought; no one ever died of anything until he was a hundred. Rikud couldn't fathom the rapid thumping of his heart. And Rikud's mouth felt dry; he wanted to swallow, but couldn't. Slowly, he took his hand off the door lever. He made his way back through the tunnel and then through the room of machinery and finally through the little room with the confusing voice to Crifer.