He reached for the ondometer. Carefully, slowly, he "tuned up" the wave-lengths; up, up to five thousand metres, then back again; he ran the whole gamut of the wireless scale. Out, ever out into the thickening gloom, across the void and vacancy of the dead world, he flung his lightnings in a wild appeal. His face grew hard and eager. "Anything? Any answer?" asked Beatrice, laying a hand upon his shoulder--a hand that trembled. He shook his head in negation. Again he switched the roaring current on; again he hurled out into ether his cry of warning and distress, of hope, of invitation--the last lone call of man to man--of the last New Yorker to any other human being who, by the merest chance, might possibly hear him in the wreck of other cities, other lands. "S. O. S.!" crackled the green flame. "S. O. S.! _S. O. S.!_--" Thus came night, fully, as they waited, as they called and listened; as, together there in that tiny structure on the roof of the tremendous ruin, they swept the heavens and the earth with their wild call--in vain. Half an hour passed and still the engineer, grim as death, whirled the chained lightnings out and away. "Nothing yet?" cried Beatrice at last, unable to keep silence any longer. "Are you quite sure you can't--" The question was not finished. For suddenly, far down below them, as though buried in the entrails of the earth, shuddered a stifled, booming roar. Through every rotten beam and fiber the vast wreck of the building vibrated. Some wall or other, somewhere, crumbled and went crashing down with a long, deep droning thunder that ended in a sliding diminuendo of noise. "The boiler!" shouted Stern. Off he flung the head-piece. He leaped up; he seized the girl. Out of the place he dragged her. She screamed as a huge weight from high aloft on the tower smashed bellowing through the roof, and with a shower of stones ripped its way down through the rubbish of the floors below, as easily as a bullet would pierce a newspaper. The crash sent them recoiling. The whole roof shook and trembled like honey-combed ice in a spring thaw. Down below, something rumbled, jarred, and came to rest. Both of them expected nothing but that the entire structure would collapse like a card-house and shatter down in ruins that would be their death. But though it swayed and quivered, as in the grasp of an earthquake, it held. Stern circled Beatrice with his arm. "Courage, now! Steady now, _steady!_" cried he. The grinding, the booming of down-hurled stones and walls died away; the echoes ceased. A wind-whipped cloud of steam and smoke burst up, fanlike, beyond the edge of the roof. It bellied away, dim in the night, upon the stiff northerly breeze. "Fire?" ventured the girl. "No! Nothing to burn. But come, come; let's get out o' this anyhow. There's nothing doing, any more. All through! Too much risk staying up here, now."