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!