are not tied together in
fixed proportions in such a way that, when there is more of one of
them used, there is _proportionately_ more of the other. Moreover,
when a unit of one of them abandons a piece of land and goes
elsewhere, there is no probability that exactly one unit of the other
will do the same. There is, indeed, no such thing as a dual unit of
labor and capital that can be thought of as moving to and fro among
different employments till it finds the point at which, as a dual
unit, it can create its largest product. These two agents so locate
themselves that a final unit of each one, separately considered,
produces as much where it is as it can produce anywhere else.

It is, however, to be noted that the amount of labor that can
profitably be employed on a piece of land grows larger the more
capital there is employed in connection with it. An acre of land and a
thousand dollars' worth of auxiliary funds can enable more men to get
good returns than can an acre combined with a fund of five hundred
dollars. Conversely, the more men there are working on the area, the
more auxiliary capital it pays to use there. If there are five men
working on a small field it may be that a thousand dollars may be well
invested in aiding them, while with only one man it would not pay to
use so large an amount. The capital and the labor, as it were, attract
each other. Additional capital attracts further labor, and _vice
versa_, till a condition is reached in which neither of them
can so well be used on that particular piece of land as it can
elsewhere. Each one has then been used on this area up to its own
intensive-marginal limit. So also when one of these agents betakes
itself to marginal land, it attracts the other agent thither. When
there are ten men on the poorest piece of land in a locality, it is
possible to make a considerable amount of capital at that point pay
the return generally prevailing, whereas only a small amount would pay
it if there were only five men working. With a thousand dollars
invested on that land more laborers will be lured thither by the
prospect of fair returns than would be lured thither if there were
only half as much capital. The general apportionment of both agents
tends to be such that a unit of either is as well off on one piece of
land as on another, and each is as well off at the extensive margin of
cultivation of land as it is on the intensive margin.

_Labor and Capital combined in Vary