METHOD OF PERIODS BY VOLUME. 315 



shiftings indicated in the general working plan, the volumes 

 .allotted to the several periods stand as follows : — 



Periodic Yield. Annual Yield. 



Period I. — 189,393 cubic feet. 9,470 cubic feet. 



„ II. = 195,474 ,, ,, 9,774 „ 



,, 111.^173,919 ,, ,, 8,696 ,, 



„ IV. = 188,240 „ „ 9,412 „ 



¥. = 194,845 ,, ,, 9,742 „ 



Total = 941,871 „ ,, 9,419 



An attempt to equalise the returns further would necessitate 

 the cutting up of compartments, which is not desirable. 

 The areas placed into the several periods 



Is are- 

 Period I. = 36"00 acres. 

 ,, 11. = 34-02 ,, 

 „ III. = 27-30 „ 

 ,, lY. = 29-05 ,, 

 „ Y. = 33-78 ,, 



Total =160-15 ,, 

 Mean periodic area = 32*03 ,, 



It is evident, that fresh shiftings will have to be made later 

 on, so as to equalise the returns during the second rotation. 



h. Merits of the JMhod 

 The method has this advantage over the method by area, 

 that it gives during the first rotation equal, or approximately 

 equal, periodic returns; it considers the interests of the present 

 generation more fully. On the other hand, the estimate of the 

 future returns is more or less problematic, so that the equali- 

 sation of the returns for a whole rotation ahead is a very 

 uncertain operation. It shares with the method by area the 

 disadvantage, that a proper grouping of age classes is generallj' 

 beset by difficulties. It also drags a surplus of growing 

 stock over a whole rotation. 



