Constructing Volume Tables. 



217 



Two tables which serve admirably, and which offer an inter- 

 esting contrast, are that for Western Larch in Flathead County, 

 Montana, and that for Douglas Fir in Freemont County, Idaho, 

 both published by the U. S. Forest Service (Form 874 d and 

 874 j). The former is based on measurements of 1,394 trees, 

 and shows every evidence of careful workmanship, while the 

 latter, though undoubtedly constructed with equal care, is based 

 on but 486 trees. 



The following tables of frustrum form factors have been de- 

 rived from these. Every fifth inch class only was computed, as 

 this was quite sufficient to show the trend of the values. The 

 figures were obtained as follows : The volumes in board feet of 

 the frustrum were computed by calculating the top diameters of 

 each of their 16 foot sections, and applying the same log rule 

 as that used in the volume table under consideration; (inter- 

 polations to the nearest tenth of an inch were, however, applied) ; 

 these frustrum values were then divided into the corresponding 

 values in the volume tables, the quotients being the values of the 

 frustrum form factors. 



Table of Frustrum Form Factors. 



Western Larch, Flathead County, Montana. 

 Number of 16 foot losrs. 



D. B. H. 



12 



15 

 20 



25 

 30 



Douglas Fir, Freemont County, Idaho. 



2 3 



.41 .66 



•97 -94 



1.54 1-04 



I-I5 



1.24 I 



Number of 16 foot logs. 

 456 Average for all heights. 



Average for all diameters, .97 i.oi 



.91 

 .91 

 • 95 

 ■93 



.91 

 .91 



.65 



.96 

 1. 17 



.98 

 1.02 



• 96 



