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such as iron and copper are produced reflect not only

rates of current production, but also the rate at which

new capacity for increased future production is formed.

 A simple, straightforward analysis of the

relationship between production of any one year and the

demand for structural materials during that year under-

states the importance of structural materials to the

total production of that period. The amounts of structural

materials "consumed" during the production of any given

year reflect only additions to the stock of materials

in use, and it is the concept of total "materials in

use" that is important.

 During any given year a certain amount of material

is processed into forms from which useful implements

are fashioned. Since such items usually are useful for

a long period of time, materials included in them also

are useful for the same period. Thus, the need for

structural materials in the productive process is the

need for materials in use, those incorporated in

buildings and machinery. Comparing "apparent consumption"

of structural materials to the overall output of any

given year is as misleading conceptually as comparing

production for any given year to the amount of capital

formation that occurred during that year.

 The stock of capital goods used during a

 given year, less the amount lost through wear or discard,