Tiny motes hovered even there, where the smallest of visible specks was a ten-man cruiser. And one of the biggest of the aircraft came gingerly up to the very inner edge of the lattice-work of fog and hung motionless, holding itself aloft by powerful helicopter screws. Men were working from a trailing stage--scientists examining the barrier even hexynitrate would not break down. * * * * * Thorn set to work. He had come toilsomely to the neighborhood of the rocket-ship because he would have to do visual signaling, and there was no time to lose. The dome of force was transparent. The air fleet would be trying to communicate through it with the Martians they believed were in the rocket-ship. Sunlight reflected from a polished canteen would attract attention instantly from a spot near the red monster, while elsewhere it might not be observed for a long time. But, trying every radio wave-band, and every system of visual signaling, and watching and testing for a reply, Thorn's signal ought to be picked up instantly. He handed his pocket speech-light receptor to Sylva. It is standard equipment for all flying personnel, so they may receive non-broadcast orders from flight leaders. He pointed to a ten-man cruiser from which shone the queer electric-blue glow of a speech-light. "Listen in on that," he commanded. "I'm going to call them. Tell me when they answer." He began to flash dots and dashes in that quaintly archaic telegraph alphabet Watch fliers are still required to learn. It was the Watch code call, sent over and over again. "They're trying to make the Martians understand," said Sylva unsteadily with the speech-light receiver at her ear. * * * * * Flash--flash--flash.... Thorn kept on grimly. The canteen top was slightly convex, so the sunlight-beam would spread. Accuracy was not needed, therefore. He covered and uncovered it, and covered and uncovered it.... "They answered!" said Sylva eagerly. "They said 'Thorn Hard report at once!'" There was a hissing, roaring noise over the hillside, where the red rocket-ship lay. Thorn paid no attention. He began to spell out, in grim satisfaction: "R-o-c-k-e-t s-h-i-p i-s--" "Look out!" gasped Sylva. "They say look out, Thorn!" Then she screamed. As Thorn swung his head around, he saw a dense mass of white vapor rushing over the hillside toward them. He picked Sylva up in his arms and ran madly....