Sec. 3] WEALTH 9

In such cases we say that the article is measured
by number. But “number” is by no means peculiar to the
last-named case. All measurement implies both an abstract
 number, and a concrete unit, as “ten screws,” “six
eggs,” or “four pounds-of-granulated-sugar.”
The last example suggests that in order to specify fully
the unit of any kind of wealth, it is necessary to enumerate
its particular attributes, or enough of them to distinguish
it from other sorts of wealth with which it may become confused.
 Thus, it is often necessary to specify what “grade”
or “brand” is meant, as “Grade A,” “Eagle Brand,”
“Lackawanna” coal. Sometimes the special sort is denoted
by a trade mark or hallmark. Tt is in this way that the
attributes of particular kinds of wealth enter into the consideration
 of economic science, and not, as some have erroneously
 supposed, separately as an “immaterial” sort of
wealth. The “fertility” of land is not to be counted as
wealth apart from the land itself ; it is the “fertile land”
which is wealth. The “skill” of a mechanic is not wealth
in addition to the man himself ; it is the “skilled mechanic”
 who should be put in the category of wealth.
Of course, the number expressing the measure of wealth
may be unity, as for instance, “one dwelling.” Sometimes
there is only one article of the particular kind in existence.
There is but one Battery Park, one Buckingham Palace,
one Koh-i-noor diamond, one Rhynd papyrus. Dealers
call such articles “uniques.” Strictly speaking, every article
 might be called a unique, even as no two grains of
wheat are precisely alike; but for practical purposes we

overlook minor differences and regard articles sufficiently
similar as homogeneous.

§ 4

Thus each individual kind of wealth may be measured in
its own special unit, — pounds, gallons, yards; but for most
purposes it is more important to measure the value of wealth,