Sec. 7] WEALTH 15 
in the mind of man, but purely objective, as money value, 
or wheat value. It has, of course, subjective causes, but 
these do not concern us yet.! 
The measurement of wealth in “value” has this great 
advantage over its measurement in ‘quantity,’ that it 
translates the many kinds of wealth into a single kind. 
All the items in the third column of the inventory are thus 
expressed in a common unit, the bushel. We may conse- 
quently add together this column and obtain a single sum, 
namely, 14,410 bushels; but summation of the first column 
is impossible, because shoes, pounds of beef, houses, and 
bushels of wheat are incommensurable. We see here one 
of the important functions of money ; it brings uniformity 
of measurement out of diversity. 
But, although this reduction to a common measure is 
practically convenient, it would, of course, be a great mis- 
take to suppose that it gives what may be called “the true 
measure of wealth.” “The value of wealth” is an incom- 
plete phrase; to be definite we should say, “the value of 
wealth in terms of gold,” or in terms of some other particu- 
lar article. We cannot, therefore, use such values for 
comparing different groups of wealth except under certain 
conditions and to a limited degree. To compare the 
wealth-values of America and England, of Ancient Rome and 
Modern Italy, of Carnegie and Croesus, will give different 
results according to the standard of value employed. 
§8 
We have seen how to measure the three magnitudes,— 
quantity, price, and value of wealth. This measurement 
is, practically, a very inaccurate affair. The degree of ac- 
curacy attained is exaggerated in the minds of most per- 
sons, even including business men. In measurements of 
quantities of wealth there are two sources of error, for every 
! Further explanation as to the dimensions of the quantity, price, 
and value of wealth are given in the Appendix to Chap. I, § 1.