ON MEASURES OF VALUE. 95

tion we must possess an object of invariable
value.
Let us examine, therefore, how far measuring
value and measuring space are similar operations.
 In every case of measuring we merely
ascertain ratios—the ratio which one thing
bears to another. In measuring the length
of an object we find what ratio it bears to
the length of some other object, or in other
words, how many times one is contained in the
other. We measure the longitudinal extension
 of a piece of timber, for example, by a footrule;
 that is, we find how often the length of the
latter is contained in the former, and this is
effected by the actual application of the rule to
the timber. It isa physical operation, by which
we obtain the knowledge of a fact before unknown,
 the ratio of length subsisting between
the object and the instrument we employ.
In measuring value, what resemblance to this
operation can possibly be discovered? We may
place two objects by the side of each other, or
apply one to the other in any way we please,