obtain correct figures on this subject. The same ideas might reasonably be considered to obtain with respect to census enumeration of other branches of the national wealth. It is easy to see why this should be so. When it is left to thousands of people to fill out the blanks of questionnaires on this subject, there are innumerable chances of misunderstanding, differences of opinion, self deception, etc., that operate to prevent correctness of totals, which may happen to be correct only by accident.
Nevertheless, given substantially correct physical data it is possible to arrive at fairly good approximations of the national wealth in many particulars by the application of engineering methods. The consulting engineer who is employed to value the property of a corporation pays but little attention to book values. He goes over the books to see what the corporation thinks it has and then examines its properties to ascertain what really exists, and finally he puts his own valuations upon what exists according to the economic standards of the time or what he foresees. This sometimes involved either the writing up of property, because of enhancement of value, or its writing down because of impairment. Writing down may not be based merely upon deterioration. Property that is in perfect physical condition may perhaps lose all value by reason of obsolescence; or it may lose value because of the existence of more of that kind of property than is required, with the result of there being no further use for the service of some of it. Economically property for which there is no use may have no value except what may result from the scrapping and salvaging of its materials. The percentage of recovery under such
