With a declining marginal product of labour curve, rent was the surplus above the ordinary wage line up to the equilibrium point on the 'sterile land which it only just pays to take into cultivation' (ibid., p.
(16) The marginal product of labour curve for the first piece of land is apc.
Given the assumption that each additional unit of the variable input will produce a smaller increment of output, the marginal product of labour curve is explained by the technical relation between the two variables.
The differential fertility of the two pieces was represented by the different heights and particular shapes of the declining marginal product of labour curves. With population given, the 'secondary' component of the explanation for Jevons's predecessors now became the explanation.
Using this relationship, we can derive a conventionally sloped demand for labour curve, shown as [N.sup.d] in Figure 1(d).
However, the movement up the demand for labour curve [N.sup.d] as a result of the increase in the real wage will induce an equal increase in the marginal product of labour.
Other things being equal, and after the usual gestation lags, the results will be upward shift in the production function of Figure 1(c), a rightward shift in the domestic demand for labour curve in Figure 1(d), and a rightward shift in the vertical aggregate supply curve of Figure 1(a).
However, to the extent that the receipt of unearned income by households leads to a reduction in the supply of labour, there will be a leftward shift in the supply of labour curve of Figure 1(b).
Adding AB to the domestic demand for labour curve [N.sup.d] yields the "stepped" total demand for labour curve [N.sup.d+quota].
An increase in the foreign real wage will raise the height of the step in the total demand for labour curve, but this will not affect the domestic real wage, and thus it will not affect domestic employment and output.