236 VALUATION, DEPRECIATION AND THE RATE-BASE 
commodity or of a service is to be ascertained and its sale price 
is to be fixed. The cost records should be so kept that they 
will give all needed information relating to past financial history 
as well as to the current cost of operation. 
Any reduction in the value of an operative property such as 
may result from an advance in the art of the manufacture of 
its output or due to decrease in value of real estate and like 
causes, may result in an operating loss. In the case of a public 
service corporation where the investment is of real concern, such 
possible reduction of value is one of the elements covered by 
the hazards of the business and should be forestalled or should 
in the course of time be amortized by the excess of earnings 
over and above earnings on ordinary safe investments. 
Any increase in value, no matter what it may result from, 
belongs among the earnings. Despite the rulings which have 
been had on this point by competent authority, it would seem 
preferable not to include appreciation in the rate-base but as 
elsewhere suggested to permit earnings that will give the owner 
a limited share in the general prosperity of the community.