Let us assume, as Ricardo did, that first-class land yields a bushel of corn as the result of ten hours’ work, the corn selling for ten shillings a bushel.[323] In order to supply a population that is increasing in accordance with the Malthusian formula, land of the second class has to be cultivated, when the production of a bushel requires fifteen hours’ work. The value of corn will rise proportionately to fifteen shillings, and landed proprietors of the first class will draw a surplus value or a bonus of five shillings per bushel. So rent emerges. Presently the time for cultivating lands of the third class will approach, when twenty hours’ labour will be necessary for the production of a bushel. The price of corn goes up to twenty shillings, and proprietors of the first class see their gift increased or their rent raised from five to ten shillings per bushel, while the owners of the second-class land obtain a bonus of five shillings per bushel. This marks the advent of a new class of rent-receivers, who modestly take their place a little below the first class. The third class of landowner will receive a rent whenever the cultivation of fourth-class land becomes a necessity.[324] It has been said in criticism of the theory that the hierarchy of lands has simply been invented for the purpose of illustrating the theory. But what Ricardo has really done is to put in scientific language what every peasant knows—what has been handed down to him from father to son in unbroken succession, namely, that all land is not equally fertile. Ricardo, so often represented as a purely abstract thinker, was in reality a very practical man and a close observer of those facts that were then occupying the attention of both public and Parliament. High rents, following upon high prices, constituted the most important phenomenon in the economic history of England towards the end of the eighteenth and the beginning of the nineteenth centuries. Right through the eighteenth century—that is, up to 1794—the highest price paid for corn was only a few pence above 60s. per quarter. But in 1796 the price rose to 92s., and in 1801 it reached 177s.—nearly three times the old price. The exceptionally high price, due to extraordinary causes, chief among them being the Napoleonic wars and the Continental blockade, could not last long, although the average during the years 1810-13 remained as high as 106s.[325]