II.

Rent is equal to production minus the marginal production.

Let productiveness mean the production from unit-area of ground, and let it be represented by y, and the marginal productiveness by g. Further, let dR/dx = z. Then we may write y = g + z + f (x); so that the profit after the rent has been paid is g + f(x); but at the margin no rent has to be paid, so that the profit there is g. Now, if equal areas of land be taken at the margin and at any other point, we have—

1/C.dC/dt = 1/C′.dC′/dt

—here I use C and C′ to include not only capital, but also labour—

∴ g + f(x)/C = g/C′;

or (C - C′)g = f(x)C′.