OF VALUE,

97

first to one and then to the other: it is far from
being so much as this: it is merely like calculating
 the ratio of length between the two
pieces of timber, after we are informed how
many feet are contained in each. For of each
commodity A and c the value in relation to B
must be given, or, in other words, their value
must be expressed in a common denomination,
before their mutual relation can be ascertained ;
just as in the case supposed the relation of each
piece of timber to the foot-rule must be given,
before their relation to each other can be deduced.
 The actual application of the foot rule
is that part of the process which is alone entitled
 to the appellation of measuring, the rest
being mere calculation, but to this there is nothing
 at all analogous in any possible attempt
to ascertain value. The way in which the
commodity B would be used, in the above
instance, is in truth as a medium of comparison,

 not a measure, yet it is the only process
which bears any analogy to measurement.
It appears, therefore, that all we can under-