The trick, above cited, of supporting a child in mid-air, was performed by Houdin at the time when the inhalations of ether for purposes of insensibility were first introduced. This idea was in the minds of the audience, and magical effects were readily attributed to etherization. Accordingly the trick was announced as "suspension in equilibrium by atmospheric air through the action of concentrated ether," and so successfully was this aspect of the trick accepted that protests were sent in against "the unnatural father who sacrificed the health of his poor child to the pleasures of the public." In the same way, Kellar introduces a "thought-reading" performance, by going through the movements of hypnotizing the lady who assists in the trick; this enables him to present the phenomenon in a mysterious light, and incidentally his manipulations furnish the opportunity to connect the end of a speaking-tube concealed in the lady's hair with another portion attached to the chair. In brief, the effect of a trick depends more upon the receptive attitude of the spectators than upon what is really done. "Conjuring," Mr. Triplett observes, "is thus seen to be a kind of game of preperception wherein the performer so plays upon the psychical processes of his audience that the issues are as he desires." There is, too, a class of tricks which illustrate a process, the reverse of this; and which depend for their éclat upon making the issues coincide with the apparently freely expressed choice of the spectator, while really the performer as rigidly determines the result as in all other cases. One of the best of these proceeds by collecting some eight or nine questions prepared by as many persons in the audience, then placing them in a hat, drawing out one at random, and finding the answer to the question thus selected written on the inside surfaces of a pair of slates. The deception begins in the substitution for the collected slips of paper, of the same number of slips all containing the same carefully prepared question; the production of the writing on the blank slate is a chemical technicality. It is a similar result that is obtained in forcing a card; or when the conjurer asks the audience to select one of a group of similar objects, and then himself decides whether the selected object shall be used for the trick or discarded; likewise, when a magic bottle is presented from which any desired variety of liquor may be produced, it is easy to suggest the choice according to the available possibilities. There is thus an imitation of the psychological factors as well as of the objective factors of real experience; and both are utilized in the deceptions of the professional conjurer.