MODIFICATIONS OF GENERAL METHOD. 51 



accuracy being obtained by joining all classes into one group. 

 In this latter case the method is known as " the method of the 

 arithmetical mean sample tree." 



Example. In order to illustrate this and the methods to be 

 described hereafter, one acre of Scotch pine wood, 70 years 

 old, was measured, and twenty-three sample trees of various 

 diameters felled and measured. Only timber down to 3" 

 diameter at the small end has been included in the account. 

 The wood is situated in the Cooper's Hill School forest at 

 Caesar's Camp, on gravelly sand, with a fair layer of humus, 

 showing a quality between III. and IV. according to Weise's 

 yield tables. The statement on pp. 52 and 53 illustrates the 

 procedure which has just been described. 



2. Modifications of the Method. 



It has been shown above that the volume of a wood is repre- 

 sented by the formula : 



F=F 1 +F 8 +F,+ . . . = v 1 x 



rr o o 



It is obvious that, as long as the fractions ^ -, , 



differ, the volumes of the sample trees in the several classes 

 must be measured separately. In order to avoid this incon- 

 venience, it has been proposed to fix the number of sample 

 trees in each class so, that 



>Si Of> OQ 



- = =-- = . . . = a constant = c, 

 s l s. 2 s s 



when the above formula reduces to : 



V=(v 1 + v 2 + v 3 + . . .)xc. 



By following this method it is not necessary to keep the 

 sample trees separate ; they can be thrown together and 

 measured in one lot. This is a great convenience, which saves 

 also much time. The volume of all sample trees multiplied by 

 the constant c gives the volume of the wood. In this way a 

 modification of the general method has been elaborated, which 

 is known by the name of Draudt's method. 



E 2 



