27 



Calculation of Quantity of Wood. 

 Ci= 27-33 X -»= 1,431 eft. 

 C2= 112-88 X ^;^9J5= 5,885 „ 

 C3=196-84x ^^ = 5,482 „ 



12,798 „ = wood of stems. 

 Add 4% 552 „ = „ „ branches. 



Total Wood . 13,350 ., 



Calculation of Average Stems, 

 ai = ^' = 0-6171 sq. ft. and gi=38 in. 

 a.= ^^=1-1890 „ „ g.= 52„ 

 as = ^ = 2-0729 „ „ g3=69 „ 



7. Survey bi/ Girth-gradations. Methods of Draudt,Urich, and 

 Eartig. 



"Whenever it is impossible to determine accurately the average 

 tree even for separate girth-classes, it is necessary to adopt as 

 the basis of survey girfch-gradations (see page 13, I A ay), 

 which obviously reqoire the measurement of a larger number of 

 sample stems than the method just described, the number for each 

 gradation being proportional to the total number of stems com- 

 prised in that gradation. 



Several methods of survey by girth-gradations have been 

 devised, but we will descri be here only those of Draudt, Urich, and 

 Robert Hartig : — 



Dratjdt's Method. 

 In this method a certain proportion, say the Mh part, of all the 



