over them like a veil, and he fell heavily, a neat bullet hole square between his eyes.

Hilary shoved the gun back in his blouse, and stared alternately at the huddled form of the grotesque being and all that remained of Amos Peabody. The old President had saved his life at the cost of his own. Instinctively his hand went up in formal salute to the gallant old man.

Grim Morgan shook him by the shoulder.

"Man," he said quietly, "we have killed a Mercutian guard. Within the hour we shall be dead men too."

Hilary looked up at him sharply.

"A Mercutian," he echoed. "You mean—"

"That for three years now the Earth has been a conquered province of these devils from Mercury," Grim interposed swiftly. "We have committed the unforgivable offense and must pay for it."

ilary glanced swiftly around. The express conveyor was clear of passengers for over a hundred yards each way. All the people within range had cleared off when Hilary had attempted to release Peabody. The small figure of a man got up from his chair beyond the charmed circle, and was threading his way forward. The local conveyors seemed to be moving backward at graded speeds. Beyond was the open country, gradually thickening into scattered rows of crystal buildings. They were in the suburbs of Great New York. Within ten minutes the conveyor terminal would be reached.

Hilary's eyes flicked speculatively to the tiny cigar-shaped boat in which the dead guard had flown down to them. Its smooth gray-gleaming surface was devoid of wings or other lifting devices. Only a fan-shaped fin projected from the stern like the tail of a fish. The cockpit, if such it could be called, was tiny, just ample enough to accommodate the Mercutian's girth. The sunlight dazzled back from a bewildering jumble of tiny lenses inset in the instrument board. Arranged along the hull, on either side, were larger disks of the same quartz-like material.

"Let's get away in the flier," he said.

"Can't," Grim said. "Those lenses you see on the instrument board are the controls. No one knows how to operate them except the Mercutians. Our people managed to capture a few, but couldn't do a thing with them."

Hilary stared at the motionless flier with interest. "What are those round glass disks stretched along the hull in a double row?" he asked. "They look like burning glasses."

"That's just what they are," said Grim sadly. "The top row are sun-lenses, that throw a terrible ray for a distance of two to three hundred feet. Melts everything in its path—men trees, rocks even. You saw one in action in the sun-tube with which poor old Peabody was cut in half. The lower row of lenses on the flier are search beams."

"Search beams?" Hilary echoed inquiringly.

"Yes. They act like X-rays, more powerful though, and with the further property of rendering everything they touch transparently crystal for depths of ten to fifteen feet. Lead is the only element they can not penetrate. Another secret our scientists can not fathom, so they talk learnedly about the stream of rays polarizing the structure of matter along a uniaxis."

"Can't those lenses be duplicated, and turned as weapons against the Mercutians?"

"No. They are made of a peculiar vitreous material native to Mercury."

"And no one has found out the principle on which they work?"

"Well, there have been theories. We haven't many scientists left, you know. But the most popular one is that these lenses have the power of concentrating the rays of the sun to an almost infinite degree, and then spreading them out again, each individual beam with the concentrated energy of the whole. Some new way of rearranging quanta of energy."

"Hmm!" Hilary's brow was wrinkled. For a long moment he stared and thought.