The giant computer was only partly the work of man. Its prototype, a far simpler machine, had furnished most of the circuit equations and was largely responsible for the final design. The men who built, operated and maintained Urei had had but the most nebulous conception of the infinitely complex nature of the completed mechanism. There were blueprints and drawings, of course, but no one human brain could encompass so much territory. Urei's operational crew was comprised of specialists in this and specialists in that, physicists, chemists and technicians; while among them they knew every circuit, every chemical reaction, every relay and every memory cell, there was no ground upon which they could meet and understand just what Urei was and what he could do. Urei alone knew the answers, and he wasn't telling unless someone was smart enough to ask him--except, of course, where his own welfare was involved. It was invariably he who detected weakness and wear, indicating the need for replacement parts by means of a complicated panel in the control room. It was he, also, who drew plans and typed suggestions for the incorporation of improvements in the design and manufacture of those parts. The first time he did that, quite a furor was created. Immediate, frenetic debating tried to decide the question of whether Urei had inexplicably acquired sentience. But Urei had anticipated all the pother, knowing humans fairly well, and only designed when a part needed replacing. His masters were thus able to reason that this apparently new function was one which had been built into him purposely. And while the debating continued desultorily, nobody seriously thought that Urei was sentient. It was conceivably within the ability of a machine which could solve abstruse problems in quantum mathematics, to design a slightly better relay than the one it had been using. Urei was merely replacing himself as he had been designed to do--not acquiring any new faculties. Yes, he was within his scope of activity--though quite a few were secretly annoyed by the fact that the problem had not been put. Urei didn't concern himself with anybody's worries; he merely noted them, remembered what had caused them, and then made sure an adequate explanation was available. This was quite easy, since he had discovered that he could superimpose his thoughts on the neural paths of humans. With care he could also take over their motor centers and cause them to do things he wanted done. But he didn't do that often, for every now and then his impatience caused him to make people do things they would not have done if left alone. That didn't matter, usually, but sometimes one of them would recognize the compulsion as being an external thing and be troubled by it. * * * * *