136

ON MEASURES

of value, is the mutual relation of two commodities
 from their separate relations to a third.
It follows, that if we wish to ascertain the
state of comfort or luxury in which any class
of people lived at any assigned period, there is
no possible method of effecting the object, but
ascertaining from the proper documents the
amount of their incomes, and then, particular
by particular, the relation which these incomes
bore to commodities. If the incomes are
stated in corn, or silver, nothing can be inferred
from the statement, as to their power over
other things. Supposing the income to be a
certain amount of money, then the inquirer
must find records of the prices of those articles
 to which his curiosity is directed, and a
simple calculation will teach him the power of
the income to command them.
If he wishes, for example, to ascertain the
condition of the labouring class at any given
period, he must first find the rate of wages, or,
in other words, the mutual relation of labour
and money. This is one step in the investiga-