[Footnote 157-5: In the beginning of the eighteenth century, the counties in the neighborhood of London addressed a petition to Parliament against the extension of the building of turnpike roads which caused their rents to decline, from the competition of distant districts. (_Adam Smith_, Wealth of Nat., I, ch. 11, 1.) Compare _Sir J. Stewart_, Principles, I, ch. 10. Improvements in transportation which affect the longest and shortest roads to a market in an absolutely equal degree, as, for instance, the bridging of a river very near the market, leave rent unaffected. (_von Mangoldt_, V. W. L., 480.)] [Footnote 157-6: _Malthus_, Principles, 231 ff. If the laboring class were to become satisfied with living on potatoes instead of meat and bread as hitherto, rents would immediately and greatly fall, since the necessities of the people might then be obtained from a much smaller superficies. But after a time, the consequent increase in population might lead to a much higher rent than before; since a great deal of land too unfertile for the cultivation of corn might be sown with potatoes, and thus the limits of cultivation be reached much later.] [Footnote 157-7: In France, between 1797 and 1847, the average price of wheat did not rise at all. _Hipp. Passy_ mentions pieces of land which produced scarcely 12 hectolitres of wheat, but which now produce 20--an increased yield of 170 francs, attended by an increase in the cost of only 75 francs. (Journal des Economistes, 15 Oct., 1848.) Moreover, it may be that a not unimportant part of modern rises in the price of corn may be accounted for by the better quality of the corn caused by higher farming. (_Inama Sternbeg_, Gesch. der Preise, 10 seq.) Such facts, readily explainable by _Ricardo's_ theory, remove the objection of _Carey_, _Banfield_ and others, that the condition of the classes who own no land has, since the middle ages, unquestionably improved. Political Economy would be simply a theory of human degradation and impoverishment, if the law of rent was not counteracted by opposing causes. (_Rœsler_, Grundsätze, 210.) According to _Berens_, Krit. Dogmengeschichte, 213, the actual highness of rent is to be accounted for by the antagonism between the "soil-law (_Bodengesetz_) of the limited power of vegetation," and the "progress of civilization" (but surely only to the extent that the latter improves the art of agriculture). Thus, too, _John Stuart Mill_, Principles, I, ch. 12; II, ch. 11, 15 seq.; III, ch. 4 seq.; IV, ch. 2 ff.] [Footnote 157-8: Thus, for instance, drainage works which, where properly directed, have paid an interest of from 25 to 70 per cent. per annum in England and Belgium on the capital invested.] SECTION CLVIII.