Leighton strode to the center of the room and thence down to that end of it where the tools of his laboratory were kept. David and Una followed, enjoying the momentary relief from the scrutiny of the old savant, who was now, apparently, engrossed in his scientific apparatus. There was not much of the latter in sight, and to the novice unfamiliar with the interior of a physicist's laboratory, and who carries away a confused impression of glass and metal jars, tubes, coils of wire, electric batteries, revolving discs, and all the nameless paraphernalia of such a place, the appointments of Harold Leighton's workshop would seem simple enough. Yet, the machine before which Leighton paused comprised one of the newest discoveries in this branch of science. Its sensational purpose was to measure and probe the mind through the purely physical operations of the body. What appeared to be, at first glance, an ordinary galvanometer stood by itself on a table. Its polished brass frame, its flawless glass cylinder enclosing the coils of wire, recording discs and needle, suggested nothing more than the instrument, familiar to the physicist, by which an electric current is measured and tested. Connected with this galvanometer, however, was a curious contrivance consisting of a mirror, over the spotless surface of which, when the machine was in operation, a ray of light, projected from an electrified metal index, or finger, moved back and forth. The exact course of this ray of light, the twists and turns made by it in traversing the mirror, was transferred by an automatic pencil to a sheet of paper carried on a revolving cylinder. This paper thus became a permanent record of whatever experiment had been attempted. That the subjects investigated by this unique galvanometer were human and not inanimate was indicated by two electrodes, attached by wires hanging from the machine, intended to be grasped by the hands of a person undergoing the test. Its use, also, as a detector of human thought and emotion, and not of mechanical force, was described by its name--the Electric Psychometer. IV THE GHOST OF THE FORGOTTEN "Modern rack and thumbscrew," exclaimed David, eyeing curiously the machine whose gleaming surface of glass and polished metal was in striking contrast with the somber oratory. Harold Leighton paid no heed to the comment. He was apparently too busied with some detail in the complicated mechanism before him to attend to anything else. David and Una, on the other hand, were more amused than impressed with the odd kind of entertainment chosen for this memorable evening of their betrothal by the eccentric scientist, although every now and then some unexpected bit of irony from him came disconcertingly enough.