He turned the two enormous forces simultaneously on the point where he knew the fort was, though it was invisible behind the wall of black that protected him. From his side, the energy of the spot where all the system of Thett was throwing its forces, was invisible. Then he released them. Instantly there was a terrific gout of light on that wall of blackness. The ship trembled, and space turned gray about them. The black wall dissolved into grayness in one spot, as a flood of energy beyond comprehension exploded from it. The enormously strong cosmium wall dented as the pressure of the escaping radiation struck it, and turned X-ray hot under the minute percentage it absorbed. The triple-ray bent away, and faded to black as the cosmic force playing about it, actually twisted space beyond all power of its mechanism to overcome. Then, in the tiniest fraction of a second it was over, and again there was blackness and only the brilliant, blinding blue of the cosmium wall testified to its enormous temperature, cooling now far more slowly through green to red. "Lord--you're right, Zezdon Afthen. I'm going to sleep," called Arcot. And the ship was suddenly far, far away from Thett. Morey took over, and Arcot slept. First Morey straightened the uninjured wall and ironed out the dents. "What, Morey, is the wall of Blackness?" asked Stel Felso Theu. "It's solid matter. A thing that you never saw before. That wall of matter is made of a double layer of protons lying one against the other. It absorbs absolutely every and all radiation, and because it is solid matter, not tiny sprinklings of matter in empty space, as is the matter of even the densest star, it stops the triple-ray. That matter is nothing but protons; there are no electrons there, and the positive electrical field is inconceivably great, but it is artificial matter, and that electrical field exerts its strain not in pulling and electrifying other bodies, but in holding space open, in keeping it from closing in about that concentrated matter, just as it does about a single proton, except that here the entire field energy is so absorbed. "Arcot was tired, and forgot. He turned his magnet and his heat against it. The heat fought the solid matter with the same energy that created it, and with an energy that had resources as great. The magnet curved space about it, and about us. The result was the terrific energy release you saw, and the hole in the wall. All Thett couldn't make any impression on it. One of the rays blasted a hole in it," said Morey with a laugh. For he, too, loved this mighty thing, the almost living ideas of his friend's brain. "But it is as bad as the space defense. It works both ways. We can't send through it but neither can they. Any thing we use that attacks them, attacks it, and so destroys it--and it fights." "We're worse off than ever!" said Morey gloomily.