184 THE INCREMENT. 



or, if i = V — V, 



V — V 

 2\,=- -X 100. 



V 



The matter can be considered from a different point of 

 view, as follows : — 



Pv _ i _ r — /• 

 100 ~7 J^' 



or 



and 



'Op. = - - 1, 



1-Oi). = - 



V=:v X 1-Op,. 



This means, that the volume at the end of one year, T^, may 

 be considered as having been produced by r working for one 

 year with j;„ per cent. 



The increment per cent, is used, sometimes to calculate 

 from the present volume the increment, which is likelj' to 

 be laid on in the immediate future, but chiefly for the purpose 

 of testing the activity of the capital invested in forestry. 



The increment per cent. 2\ i^ naturally very large during 

 the early youth of a tree or wood ; but as the volume increases 

 year by year, that is to say, the denominator in the above 

 equation, while the annual increment does not increase in 

 anything like the same proportion, and in fact begins to 

 decrease comparatively early, it follows, that the increment 

 per cent, becomes smaller year by year. Heavy thinnings 

 can temporarily produce an exception to the above rule, as 

 they may retard the sinking of the increment per cent, by 

 diminishing the producing capital. 



As the determination of the increment of a single year is a 

 difficult and inaccurate operation, it is usual to determine 

 it for a number of years, 5, 10, or, generally, n years, and 

 to consider T' as the volume produced by placing r for n years 

 at compound interest, working with 2\ per cent. : — 



V = vX {1-OpJ". 



