192 THE INCKEMENT. 



This agrees with the table, as it shows 



For the period 30-40 : p = 3'10 

 40-50: p = l-98 

 or about 2'5 for the year 40. 



For final and intermediate returns : 



jj; _ 100+ S Xl00 ^100 + 51_ 2 . 52 



The table shows 



For the period 50-60 : / = 2'66 

 60-70 : / = 2-05 

 between which 2*52 lies. 



(8) The maximum quantity return will be obtained under a 

 rotation of 60 years. 



SECTION II. QUALITY INCREMENT. 



By quality increment is understood the increase in the 

 value per unit of volume. It is produced, in the first place, by 

 larger pieces of timber fetching higher prices per unit of 

 measurement, and secondly by a reduction of the cost of 

 harvesting per unit of measurement. Quality increment is 

 independent of any alteration in the general price of forest 

 produce. 



If in the course of n years the net value of the unit of 

 volume rises from q to Q, then the quality increment is 

 -= Q q, and the corresponding per cent, is obtained by the 

 formula : 



and 



or 



