QUANTITY INCREMENT PER CENT. 187 



A law of considerable importance in the preparation of work- 

 ing plans, which was discovered by Pressler, runs thus : 



" The increment per cent., in its gradual fall, is expressed for 

 the year r, in which the mean annual increment culminates, by 

 the formula 



100 

 For final yield only: .... p v = . 



For final and intermediate yields : p' v = 



where t represents the sum of all thinnings expressed in per 

 cent, of the final yield. 

 The proof is eas} T : 



The increment per cent, is, 



p v = -xlQQ. 



v 



In the year r, when the mean annual increment culminates, 

 the current annual increment is equal to the mean annual in- 

 crement, that is to say, i = - ; introducing this value in the 



T 



above formula, it becomes 



r v r 

 For final and intermediate yields let : 



T = total of intermediate yields to the year r', 

 v = final yield in the year r', 



then the maximum mean annual increment 



_v'+T 

 r' 



If p v f be the corresponding increment per cent., then 

 , v'+T 100 100 



r v r \ v 



If now t represents the per centage of T in v' t then 



T 



t ~^7 x 



