VOLUME INCREMENT PER CENT. 185 



From tliis — 



i-o,„y=': 



/ V 



and 



and 



or 



and 



p, = 100 (,^X - 1 ) , = 100 X y/- - lOQ, 



100 + ih = 100 X :/r 



\os V — log?- 



log(100+7O = 2 + 



It 



In order to avoid the use of logarithms, several formulae 

 have been evolved, which give approximately accurate results. 

 Pressler obtained such a formula by assuming, that the 

 increment during the n years is laid on in annually equal 

 quantities, and b}^ comparing the increment with the volume, 

 which is present in the middle of the period of n years. He 

 thus obtains the proportion — 



Capital : annual increment = 100 : 2)„ 



^'t-'^: 11^' -100 :iK 



and 



V - V 200 



This formula gives j^z, somewhat too small; but the difference 

 is so slight, that it can be neglected for all practical purposes. 

 Example : — 



Let r in the year 70 = 3,820 cubic feet ; 

 „ V in the year 80 = 4,260 



