VOLUME I^X•REMENT PER CENT. 183 



former would yield in each rotation 17B x 30 = 5,190 cubic 

 feet, and in seven rotations = 5,190 X 7 = 36,830 cubic feet. 

 The latter would yield in one rotation 237 X 70 = 16,590 

 cubic feet, and in three rotations = 16,590 X 3 = 49,770 cubic 

 feet, or 13,440 cubic feet more. 



The maximum for final yield only occurs earlier than that 

 for final phis intermediate yield ; the difference may amount 

 to 10 and even 20 years. 



2. Volume Increment Per coit. 



So far the increment has been expressed in actual volume. 

 In addition, it is useful to ascertain the proportion, which 

 exists between the total volume of a tree or wood at a certain 

 age and the increment laid on during the year before or 

 the following year. In order to express this proportion 

 independently of the actual volume, it is usual to give it in 

 per cents., and to call it the "increment per cent." ; by this 

 is, therefore, understood the current annual increment, which 

 is laid on by every 100 units of volume. 



If a capital, C, yields annually the interest E, then the 

 per cent., 2^, with which the capital has worked, is found by 

 the equation — 



R ^^ 

 C 100 



and 



p = y^X 100 



In the same way it may be said, if v ■= the volume of a tree 

 or wood, / = the increment added during one year's growth, 

 and />„ = the per cent., with which the capital v has worked, 

 then the following equation holds good : — 



and 



r 100' 



p, = 1 X 100 



V 



