hanged if society were static. The level of the line _AB_
represents what, under such a condition, would be the capital of a
decade. The curved line _AB'_, dipping below _AB_ and then rising
above it, expresses the fact that a single important improvement first
trenches on the amount of capital in use, and soon makes good the
deduction and makes a positive addition. It raises the sum total of
capital to the level of the latter part of the line _AB'_. The curved
line _A'B''_, first falling below _A'B'_ and then rising above it,
expresses the fact that a second improvement, made a year or two after
the first one, makes a reduction of the amount of capital as
determined by the first improvement, and later adds more than enough
to make good this reduction. A third improvement, at the end of two or
three further years, has the effect expressed by the line _A''B'''_;
that is, it first reduces the fund below the level at which at that
time it would otherwise have stood,--but by no means to the level at
which it stood when the series of improvements began,--and later
carries it above the line expressing the highest level it would,
without this improvement, have attained. In so far as these three
improvements affect the level of the social capital for the ten-year
period, it stands at the level indicated by the line _AA'A''B'''_, and
no later improvement, even at the time of its introduction, does more
than to make a small reduction of the increment of capital accruing
from the products of the earlier improvements. A series of economical
changes means a perpetual increase of the social capital as well as a
perpetual improvement in the mode of applying labor. The increments of
capital due to the earlier changes are far more than is required by
the introduction of any later one.

_The Impossibility of Reducing Capital by too Rapid Progress._--There
is a theoretical question whether this series might be too rapid to
permit this result. If the interval were a month instead of several
years, and if the amount of capital put into the new appliances were
the same that, in the figure, they are represented as requiring, the
effect would be to make twelve deductions from the amount of the
social capital in the course of a year, which would carry it some
distance below its original level, _while in this one year_ there
would have been no time for the profits to accrue in order to restore
and add to the fund. In the next year and the follow