WHEN a number of persons are assembled the mental processes of each are modified, so that his feeling, thinking and acting are different from what they would be were he alone. Each is more or less conscious of the presence of the others, and this consciousness affects in some measure his general mental state; this modification of his mental state is reflected, however slightly, in his bearing and action, and, in turn, reacts upon the mental state of those in his presence. There is initiated at once a series of interactions between the persons assembled which can not stop until they are again dispersed. This class of psychic phenomena is of peculiar interest, and increasingly so in this age of dense massing of population and of great popular gatherings.
We may for convenience divide assemblies into several classes. The two chief classes we shall distinguish accord ing to the absence or presence of a common purpose in the coming together of the people.
I. There is the purely accidental concourse. A number of persons find themselves near to one another by accident, as each pursues his individual way. They are there with no common purpose, and have no other sort of common interest in being there. They have spatial unity, so to speak; they are in the same locality at the same time, and perhaps this unity is only for the moment. Have they any psychical unity ?
Now, the proposition as to mental interaction was stated as universal, but it may fairly be questioned whether it holds good as to the accidental concourse. When, for instance to take an extreme case a number of people, each of