One is the hypothesis of telepathy. A considerable amount of respectable evidence has been brought forward in recent years to prove that one mind may directly influence another by some obscure mode of action that does not involve the known organs of expression and of perception; and much of this evidence seems to show that one mind may directly induce in another a state of consciousness similar to its own. If, then, such direct interaction between two minds can take place in an easily appreciable degree in certain instances, it would seem not improbable that a similar direct interaction, producing a lesser, and therefore less easily appreciable, degree of assimilation of the states of consciousness of the minds concerned, may be constantly and normally at work. If this were the case, such telepathic interaction might well play a very important part in collective mental life, and, where a large number of persons is congregated, it might tend to produce that intensification of emotion which is so characteristic of crowds. In fact, if direct telepathic communication of emotion in however slight a degree is possible and normal, and especially if the influence is one that diminishes with distance, it may be expected to produce its most striking results among the members of a crowd; for the emotion of each member might be expected to be intensified by the telepathic influence radiating from every other member. Some slight presumption in favour of such a mode of explanation is afforded by the fact that the popular use of the word contagion in the present connexion seems to imply, however vaguely, some such direct communication of emotion. But telepathic communication has not hitherto been indisputably established; and the observations that afford so strong a presumption in its favour indicate that, if and in so far as it occurs, it does so sporadically and only between individuals specially attuned to one another or in some abnormal mental state that renders them specially sensitive to the influence[19]. And, while the acceptance of the principle of sympathetic induction of an emotion, as an instinctive perceptual response to the expressions of that emotion, renders unnecessary any further principle of explanation, the consideration of the conditions of the spread of emotion through crowds affords evidence that this mode of interaction of the individuals is all-important and that telepathic communication, if it occurs, is of secondary importance. For the spreading and the great intensification of emotion seem to depend upon its being given expressions that are perceptible by the senses. So long as its expressions are suppressed, the emotion of an assembly does not become excessive. It is only by eliciting and encouraging the expressions of emotions that the revivalist, the political orator, or the comic man on the music-hall stage, achieves his successes. That the expressions of an emotion are