He flung back his head. High up and far away, beyond that invisible barrier against which Watch-planes had flung themselves in vain, there were tiny motes in mid-air. These were Watch planes too, hovering outside the obstacle they could not see, but which even hexynitrate bombs could not break through. And very far away indeed there was a swiftly-moving small dark cloud. As Thorn watched, that cloud drew close. As his eyes glowed, it resolved itself into its component specks. Small, two-man patrol-scouts. Larger, ten-man cruisers of the air. Huge, massive dreadnaughts of the blue. A complete combat-squadron of the United Nations Fighting Forces was sweeping to position about the dome of force above the rocket-ship.
The scouts swept forward in a tiny, whirling cloud. They sheered away from something invisible. One of them dropped a smoking object. It emitted a vast cloud of paper, which the wind caught and swept away, and suddenly wrapped about a definite section of an arc. More and more of the tiny smoke-bombs released their masses of cloudlike stuff. In mid-air a dome began to take form, outlined by the trailing streaks of gray. It began to be more definitely traced by interlinings. An aerial lattice spread about a portion of a six-mile hemisphere. The top was fifteen thousand feet above the rocket-ship, twenty-five thousand feet from sea-level, as high as Mount Everest itself.
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.