From similar considerations, it appears that many purely mechanical improvements, which have, apparently, at least, no peculiar connection with agriculture, nevertheless enable a given amount of food to be obtained with a smaller expenditure of labor. A great improvement in the process of smelting iron would tend to cheapen agricultural implements, diminish the cost of railroads, of wagons and carts, ships, and perhaps buildings, and many other things to which iron is not at present applied, because it is too costly; and would thence diminish the cost of production of food. The same effect would follow from an improvement in those processes of what may be termed manufacture, to which the material of food is subjected after it is separated from the ground. The first application of wind or water power to grind corn tended to cheapen bread as much as a very important discovery in agriculture would have done; and any great improvement in the construction of corn-mills would have, in proportion, a similar influence. Those manufacturing improvements which can not be made instrumental to facilitate, in any of its stages, the actual production of food, and therefore do not help to counteract or retard the diminution of the proportional return to labor from the soil, have, however, another effect, which is practically equivalent. What they do not prevent, they yet, in some degree, compensate for.(136) Chart VII. _Ratio of Miles of Railroad to the Areas of States and Countries—United States and Europe. The relative proportion is 1 Mile Railroad to 4 Square Miles of Area._