CURRENT RATE OF INTEREST. 163 



compound interest calculated for the end of the 

 year m = 



'op 



(d) From these amounts must be deducted all returns 

 realized between the formation of the wood and the 

 end of the year m 



T a xl'op m - a +T b xI'op m - b + . . . + T l xI'op m - l +T m . 



The forest per cent. = p f with which the invested capital 

 is working during the year ra + 1 is, therefore, expressed by 



the formula : 







(Y m+l -Y m -e)lW 



The denominator in the above formula can also be written 

 thus : 



(S C +E) (l'op m 



On reference to page 139, it will be seen that this expression 

 represents the cost value of the growing stock immediately 

 after the thinning in the year m has been made plus the cost 

 value of the soil ; hence the formula for the forest per cent. 

 reduces to 



curr. = (Y m+l -Y m -e)xWO*_ (Y m+1 -Y m -e}xlW 

 S c + m G e m F c 



By substituting the utilization value of the growing stock 

 for its cost value, the formula becomes 



* This formula differs from that usually given in continental works, which is 

 as follows : 



It is easy to show that this formula is only correct for the year in which 

 = general per cent.^?. 



M 2 



