"The discovery of a bank-note number requires a slightly different explanation. The conditions are these: The subject is intently thinking of a certain figure. His mind is in a state of expectant attention. He is waiting for but one thing in the world to happen--for another to give audible expression to the name of that which he has in mind. The instant that the conditions are fulfilled, the mind of the subject is released from its state of tension, and the accompanying nervous action causes a slight muscular tremor, which is perceived by the acute senses of the muscle-reader. This explanation applies, also, to the pointing out of one pin among many, or of a letter or a figure on a chart. The conditions involved in the tracing of a figure on a blackboard or other surface are of a like order, although this is a severer test of a muscle-reader's powers. So long as the muscle-reader moves the crayon in the right direction, he is permitted to do so; but when he deviates from the proper course, the subject, whose hand or wrist he clasps, involuntarily indicates the fact by the usual slight muscular tremor. This, of course, is done involuntarily; but if he is fulfilling the conditions demanded of all subjects, absolute concentration of attention and absence of muscular control--he unconsciously obeys his impulse. A billiard player does the same when he follows the driven ball with his cue, as if by sheer force of will he could induce it to alter its course. The ivory is uninfluenced; the human ball obeys." III. PHYSICAL PHENOMENA. 1. Psychography, or Slate-Writing. One of the most interesting phases of modern mediumship, on the physical side, is psychography, or slate-writing. After an investigation extending over ten years, I am of the opinion that the majority of slate-writing feats are the results of conjuring. The process generally used is the following. The medium takes two slates, binds them together, after first having deposited a small bit of chalk or slate pencil between their surfaces, and either holds them in his hands, or lays them on the table. Soon the scratching of the pencil is heard, and when the cords are removed a spirit message is found upon the surface of one of the slates. I will endeavor to explain the "modus operandi" of these startling experiments. Some years ago, the most famous of the slate-writing mediums was Dr. Henry Slade, of New York, with whom I had several sittings. I was unable to penetrate the mystery of his performance, until the summer of 1889, when light was thrown upon the subject by the conjurer C-- whom I met in Baltimore. [Illustration: FIG. 2. DR. HENRY SLADE.] "Do you know the medium Slade?" I asked him. "Yes," said he, "and he is a conjurer like myself. I've had sittings with him. Come to my rooms to-night, and I will explain the secret workings of the medium's slate-writing. But first I will treat you to a regular séance."