two margins of utilization of land, an
extensive and an intensive one, and that the product of labor and
capital at either of these margins may be used as a basis for
computing the surpluses which constitute the rent of the land. The
landlord gets from a good field what it produces minus what the labor
and capital that are used on this field would produce if they were
used on the poorest land in cultivation; or, what is the same thing,
he gets from the field what it produces minus what this labor and
capital would produce if they were set working somewhere on the
intensive margin of cultivation. Take the men out of this field, add
them in small detachments to the men who are already cultivating other
fields, in order that such fields may be tilled a little more
intensively, and measure the product which the laborers create when
they are so placed. Withdraw also the capital from the field, add it,
in small amounts, to the capital that is working elsewhere, and
measure its specific product. The sum of these two specific products
is the same amount that is arrived at by using the former standard.
This labor and capital, formerly used on the good field, scattered as
they now are among the users of other good land, will create the same
amount that they would have created if they had been employed on the
poorest land in cultivation. This amount is, as it were, what they
produce by their own unaided power; and whatever is produced in excess
of this amount when a good field comes to their assistance is the rent
of that field, for it is the contribution which the field makes to the
joint production. Total product of land, labor and auxiliary capital
minus the product created by the labor and auxiliary capital when
these agents are put in marginal positions equals the rent of the
land.

_The Rent of an Instrument measured from the Intensive Margin._--We
can measure the product of any instrument in this way. If it is a
ship, it takes labor to sail it and requires a considerable amount of
auxiliary capital. We must fill the bunkers with coal, stock the
steward's department with provisions, furnish and light the staterooms
and the saloons, and provide cordage and a wide variety of other ship
stores. All this labor and all this capital we could take out of the
ship and use elsewhere. We could convert them into marginal labor and
capital. We could divide them among the owners of other ships where
they would be used in a way that woul