Money is the cardinal device by which values have become rationalized and sentiments have been replaced by interests. It is just because we feel no personal and no sentimental attitude toward our money, such as we do toward, for example, our home, that money becomes a valuable means of exchange. We will be interested in acquiring a certain amount of money in order to achieve a certain purpose, but provided that purpose may be achieved in any other way we are likely to be just as well satisfied. It is only the miser who becomes sentimental about money, and in that case he is likely to prefer one sort of money, say gold, to another, irrespective of its value. In this case the value of gold is determined by personal sentiment rather than by reason. An organization which is composed of competing individuals and of competing groups of individuals is in a state of unstable equilibrium, and this equilibrium can be maintained only by a process of continuous readjustment. This aspect of social life and this type of social organization are best represented in the world of business which is the special object of investigation of political economy. The extension of industrial organization, which is based on the impersonal relations defined by money, has gone forward hand in hand with an increasing mobility of the population. The laboring man and the artisan fitted to perform a specific task are compelled, under the conditions created by city life, to move from one region to another in search of the particular kind of employment which they are fitted to perform. The tide of immigration which moves back and forth between Europe and America is to some extent a measure of this same mobility.[8] On the other hand, the tradesman, the manufacturer, the professional man, the specialist in every vocation, seeks his clients as the difficulties of travel and communication decrease over an ever widening area of territory. This is another way in which the mobility of the population may be measured. However, mobility in an individual or in a population is measured, not merely by change of location, but rather by the number and variety of the stimulations to which the individual or the population responds. Mobility depends, not merely upon transportation, but upon communication. Education and the ability to read, the extension of the money economy to an ever increasing number of the interests of life, in so far as it has tended to depersonalize social relations, has at the same time vastly increased the mobility of modern peoples. The term “mobility,” like its correlative, “isolation,” covers a wide range of phenomena. It may represent at the same time a character and a condition. As isolation may be due to the existence of purely physical barriers to communication, or to a peculiarity of temperament and a lack of education, so mobility may be a consequence of the natural means of communication or of an agreeable manner and a college education.