insect known as a death-watch. His first thought was that it could be nothing more than a mere "echo-signal," from too high intensity. His second thought convinced him that this was out of the question; too long a time had elapsed between his own send and those coherent dots and dashes creeping into his startled ear. It was an outside message, a call being intercepted by his antennæ. Yet the signal that he was reading was the same as his own "Pt-Ba," "Pt-Ba."
McKinnon's hand once more darted out to his switch, and his face was alert and changing with his changing thought as he caught up his key-lever. And again the blue spark exploded across the spark-gap, and the cabin walls threw back the lightning-like flash and pulse of the illumination. Already he had forgotten the heat, the depressing sense of frustration, the brooding consciousness of impending defeat that had weighed upon him. Switching off, he sat with inclined head, intently, raptly listening.
He was startled to feel a huge and ape-like hand suddenly take hold of his arm.
"What're you getting?" demanded the owner of the arm.
It was Ganley standing there close beside him. His dark face, wet with perspiration, shone in the strong side-light as though it had
