Though the varying strength of the vital forces of nature is thus brought to uniformity, there may be a difference in the different stages of social development as to the proportionate extent to which, in the aggregate production of wealth, these vital forces are enlisted. But as to this, there are two remarks to be made. In the first place, although in such a country as England the part taken by manufactures in the aggregate wealth production has very much increased as compared with the part taken by agriculture, yet it is to be noticed that to a very great extent this is true only of the political or geographical division, and not of the industrial community. For industrial communities are not limited by political divisions, or bounded by seas or mountains. They are limited only by the scope of their exchanges, and the proportion which in the industrial economy of England agriculture and stock-raising bear to manufactures is averaged with Iowa and Illinois, with Texas and California, with Canada and India, with Queensland and the Baltic—in short, with every country to which the world-wide exchanges of England extend. In the next place, it is to be remarked that although in the progress of civilization the tendency is to the relative increase of manufactures, as compared with agriculture, and consequently to a proportionately less reliance upon the reproductive forces of nature, yet this is accompanied by a corresponding extension of exchanges, and hence a greater calling in of the power of increase which thus arises. So these tendencies, to a great extent, and, probably, so far as we have yet gone, completely, balance each other, and preserve the equilibrium which fixes the average increase of capital, or the normal rate of interest.