Coquenil was watching closely and, through the prisoner's half shut eyes,
he caught a flash of anger, a quick clenching of the freed hands and
then--then Groener sat down.

Quickly and skillfully the assistant adjusted the leather sleeve over the
bared left arm and drew it close with straps.

"Not too tight," said Duprat. "You feel a sense of throbbing at first, but
it is nothing. Besides, we shall take the sleeve off shortly. Now then," he
turned toward the lantern.

Immediately a familiar scene appeared upon the sheet, a colored photograph
of the Place de la Concorde.

"What is it?" asked the doctor pleasantly.

The prisoner was silent.

"You surely recognize this picture. Look! The obelisk and the fountain, the
Tuileries gardens, the arches of the Rue de Rivoli, and the Madeleine,
there at the end of the Rue Royale. Come, what is it?"

"The Place de la Concorde," answered Groener sullenly.

"Of course. You see how simple it is. Now another."

The picture changed to a view of the grand opera house and at the same
moment a point of light appeared in the headpiece back of the chair. It was
shaded so that the prisoner could not see it and it illumined a graduated
white dial on which was a glass tube about thirty inches long, the whole
resembling a barometer. Inside the tube a red column moved regularly up and
down, up and down, in steady beats and Coquenil understood that this column
was registering the beating of Groener's heart. Standing behind the chair,
the doctor, the magistrate, and the detective could at the same time watch
the pulsating column and the pictures on the sheet; but the prisoner could
not see the column, he did not know it was there, he saw only the pictures.

"What is that?" asked the doctor.

Groener had evidently decided to make the best of the situation for he
answered at once: "The grand opera house."

"Good! Now another! What is that?"

"The Bastille column."

"Right! And this?"

"The Champs Elysees."

"And this?"

"Notre-Dame church."

So far the beats had come uniformly about one in a second, for the man's
pulse was slow; at each beat the liquid in the tube shot up six inches and
then dropped six inches, but, at the view of Notre-Dame, the column rose
only three inches, then dropped back and shot up seven inches.

The doctor nodded gravely while Coquenil, with breathless interest, with a,
morbid fascination, watched the beating of this red column. It was like the
beat