4. _A high efficiency of industry is dependent on many social causes making possible a great specialization._ It was said in another connection that division of labor is dependent upon the size of the market. With a large population massed at one spot, so that the demand for even the less important products is large, there may be a high specialization of industry. An increase of transportation, such as railways and telegraphs, is equivalent for many economic purposes to growth of population on one spot. In colonial days it took ten days to go from Boston to Philadelphia, and two weeks to go to Washington. San Francisco is now for many economic purposes but one fourth as far from Boston as Washington was at that time. California and the eastern states are distant only thirty minutes by telegraph and three days and a fraction by railroad, and are thus in many respects in the same market. The great development during the past century in the means of communication and of carriage has made possible, as never before, the massing of population to secure the advantages of division of labor in most lines, without meeting the hitherto insurmountable difficulty in the securing of food for such large numbers in a limited space. The population draws its food from the whole vast area; whereas it is massed at the points more favorable for other products and can make use of the most highly specialized machinery. These several conditions thus have favored the growth of large industry under a single control and direction, on a scale never before approached. These changes have brought in their train social problems connected with the concentration of economic power. It remains to be seen whether the unquestioned economies of this new organization can be retained and improved while it is divested of its evils. [Sidenote: Growing importance of directive ability]