Whenever it is essential to the greatest efficiency of labor that many laborers should combine, the scale of the enterprise must be such as to bring many laborers together, and the capital must be large enough to maintain them. Still more needful is this when the nature of the employment allows, and the extent of the possible market encourages, a considerable division of labor. The larger the enterprise the further the division of labor may be carried. This is one of the principal causes of large manufactories. Every increase of business would enable the whole to be carried on with a proportionally smaller amount of labor. As a general rule, the expenses of a business do not increase by any means proportionally to the quantity of business. Let us take as an example a set of operations which we are accustomed to see carried on by one great establishment, that of the Post-Office. Suppose that the business, let us say only of the letter-post, instead of being centralized in a single concern, were divided among five or six competing companies. Each of these would be obliged to maintain almost as large an establishment as is now sufficient for the whole. Since each must arrange for receiving and delivering letters in all parts of the town, each must send letter-carriers into every street, and almost every alley, and this, too, as many times in the day as is now done by the Post-Office, if the service is to be as well performed. Each must have an office for receiving letters in every neighborhood, with all subsidiary arrangements for collecting the letters from the different offices and redistributing them. To this must be added the much greater number of superior officers who would be required to check and control the subordinates, implying not only a greater cost in salaries for such responsible officers, but the necessity, perhaps, of being satisfied in many instances with an inferior standard of qualification, and so failing in the object.