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 consequently
 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 mistake
 to suppose that it gives what may be called “the true
measure of wealth.” “The value of wealth” is an incomplete
 phrase; to be definite we should say, “the value of
wealth in terms of gold,” or in terms of some other particular
 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 accuracy
 attained is exaggerated in the minds of most persons,
 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.