opposite reactions if the man were a true revolutionist or if he were a spy. Meyan’s pulse so strengthened and slowed—as under a pleasurable stimulus—that I felt I had received confirmation of my suspicions, though I had not then the information which would enable me to expose the man. To secure this I sought out Dmitri Vasili. He introduced me to Munikov, who had been a friend of Silber before his imprisonment and between them I got the history of Herman Silber and his daughter.

“I explained to Munikov and Vasili that the methods of the psychological laboratory would be as efficacious in picking out a spy among true men as I have many times proved them to be in convicting the criminal.

“Every emotion reacts upon the pulse, which strengthens in joy and weakens in sorrow, changes with anger and with despair; and as every slightest variation it undergoes can be detected and registered by the sphygmograph—I felt certain that if I could test the three men together by having Miss Silber tell her father’s story aloud, I could determine conclusively by comparison of the records of the two true revolutionists with that of Meyan, whether his sympathies were really with the revolutionist party. I arranged with Munikov and Vasili to come here with me tonight, and, after Meyan had arrived, they left us here and went to him as representatives of the revolutionary movement to ask his credentials.

“When he could furnish none,” Trant went on, “they proposed, and in fact forced him, into this test. It is a dangerous thing to endeavor to pass oneself off as a revolutionist, and it was safer for him to submit to a test than to have his mission frustrated by incurring not only suspicion, but possibly death. Completely ignorant of the pitiless powers of psychological methods, and confiding in his steely nerves, which undoubtedly have carried him through many less searching ordeals, he agreed. You saw how perfectly he was able to control his face and every movement of his body while the test went on. But you can see here”—Trant spread out his strips of smoked paper—“on these records, which I shall preserve by passing them through a bath of varnish, how useless that self-control was, since the sphygmograph recorded by its moving pencil the hidden feelings of his heart.

“As I lay these side by side, you can see how consistently at each point in the story Munikov and Vasili experienced the same feelings; but Meyan had feelings which were different. I did not dream, of course, when I started the test that I would discover in Meyan the same man who had betrayed Herman Silber. It was only 

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