still held under arrest, he pushed open, with an air of importance, the door of the captain's room, to which the sharp nod of the desk sergeant had directed him.
The detective's first glance showed him the room's three occupants—the huge figure of Division Inspector of Police Walker, lolling in the chair before the captain's desk; a slight, dark man—unknown to Siler—near the window; and Luther Trant at the end of the room busy arranging a somewhat complicated apparatus.
Trant, with a short nod of greeting, at once called Siler to his aid.
With the detective's half-suspicious, half-respectful assistance, the psychologist stretched across the end of the room a white sheet about ten feet long, three feet high, and divided into ten rectangles by nine vertical lines. Opposite this, and upon a table about ten feet away, he set up a small electrical contrivance, consisting of two magnets and wire coils supporting a small, round mirror about an inch in diameter and so delicately set upon an axis that it turned at the slightest current coming to the coils below it. In front of this little mirror Trant placed a shaded electric lamp in such a position that its light was reflected from the mirror upon the sheet at the end of the room. Then he put down a carbon plate and a zinc plate at the edge of the table; set a single cell battery under the table; connected the battery with the coils controlling the mirror, and connected them also with the zinc and carbon plates.
"I suppose," Siler burst out finally with growing
