132

ON MEASURES

ducing labour of the yard of cloth must be
equal to the producing labour of the 6s.; that is,
a quarter of the quantity of labour employed to
produce a yard of cloth in 1600.
It may probably be alieged, however, as an
advantage peculiar to the first case, that the
quantity of producing labour being invariable,
we are saved from all that research into its comparative
 quantity at different periods which
would be necessary on the contrary supposition.
But it is to be recollected, that the circumstance
of a commodity having been always produced
by the same quantity of labour, is an historical
fact quite as difficult to ascertain as the variations
 of another commodity. We might, it is
true, be saved from all investigation of this
nature, if there existed a commodity, which,
from some obvious and insuperable necessity,
was always the product of the same labour; yet
even this advantage is not dependent on the invariableness
 of the labour; for if, what is
equally easy to suppose, and quite as likely to
happen, we had a commodity which necessarily