For answer, they both lifted up their hands, obviously unoccupied, into the air. Even as they did so, the knocks started again, still rapid, but with a certain deliberate rhythm, and much less violent. Again they seemed to be on the underside of the table. Horst looked, with a scowl of distrust, under it to their immobile feet. The two young men glanced at each other, as puzzled and alarmed as Horst himself. “What in the name of Heaven is it?” cried Jensen. The knocks swelled suddenly louder as though in answer to his voice. “Listen!” said Horst, holding up his hand. The colour had gone suddenly out of his face, his eyes fixed themselves in a recognition charged with vague fear. “It’s----!” “Yes!” cried Jensen, “by all that’s wonderful----!” “The Morse code!” Lyngstrand completed the sentence. Once perceived, there was no doubt of it. That succession of irregular taps and pauses coming from the table as from a sounding-board was a plain language to all three of them, unmistakable, not more to be banished from cognition than the reiteration of spoken words. “But,” cried Lyngstrand, “where does it come from?--We have no wireless--and even wireless could not produce that!” “Listen!” Jensen reproved him. “It’s a message of some kind!” He glanced across to Horst who sat speechless, his face gray, his eyes terrified. “Not Swedish!--Take it down, Lyngstrand, while I spell it out!” The young man feverishly produced pencil and paper from his pocket. “Listen!” he cried. “Good God! Do you catch it?” Three sharp taps--three more widely spaced--three sharp taps again--the series was reiterated insistently--_S--O--S!--S--O--S!--S--O--S!_ “Ready, Lyngstrand?” queried Jensen in the sharp tone of a man concentrating himself for action. His comrade nodded. Jensen rapped sharply upon the table the wireless operator’s signal of reception. In immediate answer the raps from the invisible source renewed themselves, continued evidently in a message. Lyngstrand jotted down the letters as Jensen spelled them out. “‘_s-t-e-a-m-s-h-i-p_’--it’s English!” he interjected. “Got it?----” The raps had continued, noted by his brain and coalesced by it into definite words. “‘_Gloucester City_’----” “_What----?_” ejaculated Lyngstrand, in incredulous amazement, as he rapidly wrote the words. Jensen continued, his attention fixed upon the unceasing raps. “--_torpedoed 50-55 north 9-14 west--sinking fast--come quickly--done in_----” He glanced up to see Horst springing at them like a maddened animal. “Stop that!” cried the captain. “It’s a trick!--it’s a trick!” In another second he had snatched paper and pencil from Lyngstrand’s hand. A formidable series of violent crashes, emanating from walls, roof, and table, was the instant response to his action. He shrank back, appalled, crouching with eyes that searched the surrounding walls in agonized apprehension. “It’s a trick!--it’s a diabolical trick!” he muttered. “_It must be!_”