128

ON MEASURES

such a commodity as he describes would be a
measure of labour, or a medium of ascertaining
 the varying quantities of labour which
commodities required to produce them. Before
 it could be employed in regard to any object,
 the value of that object, or its relation to
the standard commodity, must be given, and
then all that could be deduced from the datum
would be the quantity of labour bestowed on
its production.
But perhaps the most remarkable circumstance
 of all is, that for this latter purpose, that
invariableness in the quantity of labour, which
he has insisted upon as so essentially requisite,
would be of no peculiar service. On the supposition
 that labour was the sole determining
principle of value, a commodity produced by
an invariable quantity of labour would afford
us no assistance even as a measure of labour,
which could not be equally derived from a
commodity the producing labour of which
was variable, provided we were furnished with
the same data.