The number of buyers and sellers that can constitute a single market is limited both directly and indirectly by the means of transportation. A dense population cannot usually be maintained without easy means of transportation to bring in a large supply of food, and to carry back manufactured goods great distances. The remarkable growth in the means of commerce since the application of steam to water traffic, and the invention of the railroad, have made it possible for goods to be gathered from most distant points. A market implies a common understanding among traders. Modern means of communication such as newspapers, post-offices, telegraph and cable, trade bulletins, commercial travelers, the consular service, and many forms of special agencies, are diffusing information widely. As a result of these changes, there has been a widening of the village-market to the markets of the province, of the nation, and finally of the world. While a part of every one's purchases continues to be made in the neighborhood, a greater and greater portion of the total business is done by traders who are widely separated and who are indeed members of the world market. Various articles produced in the same locality may seek different markets. The market for wheat may be in Liverpool, while that for fruit and eggs is in the village near the farm-house. If a given product of any community is sold in different markets, the net prices secured must be very nearly equal. [Sidenote: The conceptions normal and market price]