112

ON MEASURES

case identical, namely, invariableness during
its application to all the objects compared.
Whether an hour or a century elapses between
the successive applications of the instrument
makes no difference. The essential requisite
is the same in measuring objects in distant
ages, or objects existing at the same time.
But in the process called measuring value,
there is no application of any instrument,
and therefore, as I have already shown, there is
absolutely nothing to which the quality of invariableness
 can be attributed, or of which it
can be affirmed. The requisite condition in
the process is, that the commodities to be measured
 should be reduced to a common denomination,
 which may be done at all times with
equal facility ; or rather it is ready done to our
hands, since it is the prices of commodities
which are recorded, or their relations in value
to money. If money, therefore, is a good medium
 of comparison at one time, it is at all
times.