There is, however, this important distinction to be made: Competition in the exchanges is more intense; changes are more rapid and, as far as the individuals directly concerned, more momentous. In contrast with such a constellation of forces as we find on the exchanges, where competing dealers meet to buy and sell, so mobile a form of social organization as the crowd and the mob exhibits a relative stability. It is a commonplace that decisive factors in the movements of crowds, as in the fluctuations of markets, are psychologic. This means that among the individuals who make up the crowd, or who compose the public which participates in the movements reflected in the market, a condition of instability exists which corresponds to what has been defined elsewhere as crisis. It is true of the exchanges, as it is of crowds, that the situation they represent is always critical, that is to say, the tensions are such that a slight cause may precipitate an enormous effect. The current euphemism, “the psychological moment,” defines such a critical condition. Psychological moments may arise in any social situation, but they occur more frequently in a society which has acquired a high state of mobility. They occur more frequently in a society where education is general, where railways, telegraph, and the printing press have become an indispensable part of the social economy. They occur more frequently in cities than in smaller communities. In the crowd and the public every moment may be said to be “psychological.” Crisis may be said to be the normal condition on the exchanges. What are called financial crises are merely an extension of this critical condition to the larger business community. Financial panics which sometimes follow upon financial crises are a precipitate of this critical condition. The fascinating thing about the study of crises, as of crowds, is that in so far as they are in fact due to psychological causes, that is, in so far as they are the result of the mobility of the communities in which they occur, they can be controlled. The evidence for this is the fact that they can be manipulated, and there is abundant evidence of manipulation in the transactions of the stock market. The evidence for the manipulation of crowds is less accessible. Labor organizations have, however, known how to develop a pretty definite technique for the instigation and control of strikes. The Salvation Army has worked out a book of tactics which is very largely devoted to the handling of street crowds; and professional revivalists, like Billy Sunday, have an elaborate technique for conducting their revivals.