FORM FACTORS. 



87 



taken from the stem or branches, omitting all other 



material. 



Form factors for branch wood, fagots, or root wood only are, 

 as a rule, not used ; their volume is ascertained by utilizing 

 the results of actual fellings and determining their proportion 

 to the volume of timber. 

 As it would be highty 

 inconvenient to measure 

 the diameter, or girth, of 

 the tree close to the 

 surface of the ground, 

 where it is usually cut, 

 it has been agreed to 

 take the measurement at 

 a convenient height. 

 According as to whether 

 that point is fixed or 

 variable, the following 

 kinds of form factors 

 may be distinguished : 

 (1) Absolute Form 

 factors. The diameter 

 (or girth) is measured at 

 any convenient height 

 above the ground, and 



Fig. 24. 



Fig. 25. 



the form factor refers only to the part a of the tree above that 

 point (Fig. 24), while the volume of the piece b below it, is 

 ascertained b} 7 separate measurement and added to the rest. 

 This is evidently troublesome and takes extra time. 



(2) True or Normal Form factors. The diameter (or girth) 

 is measured at a constant proportion of the height of the tree, 

 say T Vth, aVth, etc. (Figs. 24 and 25). In this case the height 

 of the ideal cylinder is equal to the height of the tree. Such 

 form factors, it was believed, would have the advantage that all 

 trees of the same shape would have the same form factor, since 

 they have been measured at a height which bears in all cases the 



