As _Skylark Two_ approached the looming planetoid the doors of vast airlocks opened. Fifty of those massive gates swung aside before her and closed behind her before she swam free in the cool, sweet air and bright artificial sunlight of the interior. She then floated along above an immense, grassy park toward two well-remembered and beloved buildings. [Illustration: _As the tiny ship approached, the doors of vast airlocks opened._] "Oh, Dick!" Dorothy squealed. "There's our house--and Cranes! It's funny though to see them side by side. Are they the same inside, too--and what's that funny little low building between them?" "They duplicate the originals exactly, except for some items of equipment which would be useless here. The building between them is the control room, in which are the master headsets of the Brain and its lookouts. The Brain itself is what you would think of as underground--inside the shell of the planetoid." The small vessel came lightly to a landing and the wanderers disembarked upon the close-clipped, springy turf of a perfect lawn. Dorothy flexed her knees in surprise. "How come we aren't weightless, Dick?" she demanded. "This gravity isn't--_can't_ be--natural. I'll bet you did that, too!" "Mart and I together did, sure. We learned a lot from the intellectuals and a lot more in hyperspace, but we could neither derive the fundamental equations nor apply what knowledge we already had until we finished this sixth-order outfit. Now, though, we can give you all the gravity you want--or as little--whenever and wherever you want it." "Oh, marvelous--this is glorious, boys!" Dorothy breathed. "I have always just simply despised weightlessness. Now, with these houses and everything, we can have a perfectly wonderful time!" "Here's the dining room," Seaton said briskly. "And here's the headset you put on to order dinner or whatever is appropriate to the culinary department. You will observe that the kitchen of this house is purely ornamental--never to be used unless you want to." "Just a minute, Dick," Dorothy's voice was tensely serious. "I have been really scared ever since you told me about the power of that Brain, and the more you tell me of it the worse scared I get. Think of the awful damage a wild, chance thought would do--and the more an ordinary mortal tries to avoid any thought the surer he is to think it, you know that. Really, I'm not ready for that yet, dear--I'd much rather not go near that headset." "I know, sweetheart," his arm tightened around her. "But you didn't let me finish. These sets around the house control forces which are capable of nothing except duties pertaining to the part of the house in which they are. This dining-room outfit, for instance, is exactly the same as the Norlaminian one you used so much, except that it is much simpler.