Once again it is seen here that differential rent II presupposes differential rent I. The minimum output obtained from a capital of £2½, i.e., from the worst soil, is here assumed to be 4 qr. Assumed, also, is that aside from the £2½ which yield 4 qrs and for which he pays a differential rent of 3 qrs, the tenant operating with soil type D invests in this same soil £2½ which yield only 1 qr, like the same capital upon the worst soil A. This would be an investment of capital which does not yield rent, since it returns to him only average profit. There would be no surplus-profit which could be transformed into rent. On the other hand, this decreasing yield of the second investment of capital in D would have no influence on the rate of profit. It would be the same as though £2½ had been invested anew in an additional acre of soil type A, a circumstance which would in no way affect the surplus-profit and, therefore, the differential rent of soils A, B, C and D. But for the tenant, this additional investment of £2½ in D would have been quite as profitable as, in accordance with our assumption, the investment of the original £2½ per acre of D, although the latter yields 4 qrs. Furthermore, if two other investments of £2½ each should yield an additional output of 3 qrs and 2 qrs respectively, a decrease would have taken place again compared with the output from the first investment of £2½ in D, which yielded 4 qrs, i.e., a surplus-profit of 3 qrs. But it would be merely a decrease in the amount of surplus-profit, and would not affect either the average profit or the regulating price of production. The latter would be the case only if the additional production yielding this decreasing surplus-profit made the production upon A superfluous, and threw acre A out of cultivation. In such case, the decreasing productiveness of the additional investment of capital in acre D would be accompanied by a fall in the price of production, for instance, from £3 to £1½, if acre B would become the rentless soil and regulator of the market-price.