CHAPTER V. 
ON COMPARING COMMODITIES AT DIF- 
FERENT PERIODS. 
PeruaPps no part of their investigations has 
perplexed political economists more than their 
attempts to compare the value of the same 
object at different periods of time. 
It is a direct inference from the explanation 
of value in the preceding chapters, as de- 
noting a relation between two commodities, a 
relation incapable of existing when there is 
only one commodity, that it cannot exist be- 
tween a commodity at one period and the same 
commodity at another period. We cannot 
ascertain the relation of cloth at one time to 
cloth at another, as we can ascertain the re- 
lation of cloth to corn in the present day. All