They clambered wearily out onto the level sands again just as the small, blazing sun was setting. "Luck," grunted Syme. "Our only chance of getting near the city is at night." He peered around, shading his eyes from the sun's glare with a gauntleted hand. "See that?" Following his pointing finger, Tate saw a faint, ephemeral arc showing above a line of low hills in the distance. "Kal-Jmar," said Syme. Tate brightened a little. His body was too filled with fatigue for his mind to do any work on the problem that was baffling him, and so it receded into the back of his mind. "Kal-Jmar," whispered Syme again. There was no twilight. The sun dropped abruptly behind the low horizon, and darkness fell, sudden and absolute. Syme picked up the extra oxygen tank and the suitcase, checked his direction by a wrist compass, and started toward the hills. Tate rose wearily to his feet and followed again. Two hours later, Kal-Jmar stood before them. They had wormed their way past the sentry posts, doing most of the last two hundred meters on all fours. With skill and luck, and with Syme's fierce, burning determination, they had managed to escape detection--and there they were. Journey's end. Tate stared up at the shining, starlight towers in speechless admiration. If the people who had built this city had been decadent, still their architecture was magnificent. The city was a rhapsody made solid. There was a sense of decay about it, he thought, but it was the decay of supreme beauty, caught at the very verge of dissolution and preserved for all eternity. "Well?" demanded Syme. Tate started, shaken out of his dream. He looked down at the black suitcase, a little wonderingly, and then pulled it to him and opened it. Inside, carefully wrapped in shock-absorbing tissue, was a fragile contrivance of many tubes and wires, and a tiny parabolic mirror. It had a brand new Elecorp 210 volt battery, and it needed every volt of that tremendous power. Tate made the connections, his hands trembling slightly, and set it up on a telescoping tripod. Syme watched him closely, his big body tensed with expectation. The field was before them, shimmering faintly in the starlight. It looked unsubstantial as the stuff of dreams, but both men knew that no power man possessed, unless it was the thing Tate held, could penetrate that screen. Tate set the mechanism up close to the field, aimed it very delicately, and closed a minute switch. After a long second, he opened it again. Nothing happened. The screen was still there, as unsubstantial and as solid as ever. There was no change. * * * * * Tate looked worriedly at his wiring, a deep wrinkle appearing between his pale, serious eyes. Syme stood stock-still but quivering with repressed energy, scowling like a thundercloud.