ly
this term to the abiding stock of such instruments except in
connections in which the adjective is not needed, because it is clear
that the land, or ground capital, cannot be referred to. In dynamic
studies the distinction between land and auxiliary capital becomes
very important.

_How the Intensive Margin locates the Extensive One._--The labor and
the auxiliary capital that betake themselves to new land of the
inferior quality represent an overflow from the better land. As long
as men can do as well by staying where they are as they can by
migrating to new regions, where inferior lands are to be had, they
will stay; but when they incur a loss by staying, they move. What a
laborer can create by securing the use of an equipment and adding
himself to the force that is at work on some good farm, can be
approximately estimated; and if there is somewhere a piece of land not
thus far used to which he can remove, and if, by going to work upon
it, he can create any more than he created while working on the older
farm and taking his products as his pay, he will till that poor piece.
But neither he nor any one else will till a piece that is still less
productive. If any one were to set himself working on land of still
poorer quality, he would lose and not gain by the change, since there
he would produce even less than he can when he is the last man set
working on the good piece.

_To what Extent the Movement of Labor and that of Capital are
Interdependent._--The early statements of the law of rent did not
usually define the intensive margin of cultivation in connection with
labor and capital separately, but spoke of these two agents as
employed together upon land in quantities increasing up to a limit
beyond which both labor and capital would best be employed elsewhere.
The supposition that labor and capital go thus together from one grade
of land to another is only approximately accurate. If we consider one
man and five hundred dollars' worth of productive wealth as a dual
unit of labor and capital, and add such units, one after another, to
the forces at work on a tract of good land, we shall reach a point at
which it will not be profitable to increase the amount of one of the
agents, while it will still be profitable to increase the amount of
the other. It will perhaps not pay to use any more capital, but it may
still pay to add to the number of workers. On land that is tilled
more and more intensively, labor and capital