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 opera- 
tions. 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 exten- 
sion of a piece of timber, for example, by a foot- 
rule; 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 un- 
known, 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,