270 PSYCHOLOGY AND PREACHING
II. We can hardly claim to be able as yet to state the " laws " of mental epidemics. Such phenomena are too complex, the factors entering into them are too many and various to permit of accurate analysis ; and yet it is possible to formulate some of the characteristics of them which are so universal that it is hardly straining language to call them laws.
I. They are wave-like. They increase in intensity, reach a maximum pitch and gradually die away. This, as we know, is a general characteristic of feeling. Collective emo tions are rhythmical, just as the emotions of the individ ual. The waves, of course, are of very unequal height and length, according to the nature of the interests in connec tion with which they appear and the complex and sometimes obscure conditions which give rise to them. The popular excitement may run its course in a day or in a few days, or it may persist for weeks or months. And within a wave of great length are always included briefer rhythms, or shorter waves of greater intensity. When a popular mood, or long persisting trend of collective emotion, is in the ascendant, any incident or suggested idea in line with it finds open and uncritical minds, and the emotional impulse connected with this idea or incident is reinforced by the full power of the general current of feeling. If the idea or incident is a highly exciting one and it will always be more exciting under these than under other conditions the result will be a temporary intensifying of the prevailing emotion. We may speak of the general or longer wave as primary and the shorter one as secondary. For example, in the first stage of the great war the majority of the people of the United States were under the sway of a decided anti-German feeling ; but during this time several incidents of a highly exciting nature occurred. Particularly was this true of the sinking of the great steamer, Lusitania. These incidents superinduced what I have called secondary waves of extraordinary in tensity. On the other hand, any suggestion which runs counter to the prevailing current will be ineffective, or at any
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