86 MEASUREMENT OF STANDING TREES. 



which might be utilized in subsequent estimates, and thus 

 foresters arrived at the following method. 



2. Estimate of Volume by means of Form factors, 

 a. Definition and Classification of Form factors. 



Under "form factor" is understood the proportion which 

 exists between the volume of a tree and that of a regularly- 

 shaped body which has the same base and height as the tree. 

 The form factor means, therefore, a coefficient with which the 

 volume of the regularly-shaped (geometrical) body must be 

 multiplied in order to obtain the volume of the tree. 



Any regularly- shaped body, the volume of which can easily 

 be calculated by means of a mathematical formula, is suited 

 for the above purpose. In practice only the cone and cylinder 

 have been employed, and at the present time only the latter is 

 used. Let s be the area of the basal section of the tree, h its 

 height, /the form factor, and v the volume, then 



Volume of^ cylinder = sxh, 

 Volume of tree =v = sxh xf, 



and 



Form factor =/=- 



J sxh. 



The volume of the stem of a tree by itself is always smaller 

 than that of the corresponding cylinder ; hence the form factor 

 for the stem only is always smaller than 1. If the volume of 

 the branches is added, the form factor is sometimes greater 

 than 1, especially during early youth. 



Various kinds of form factors are used in forestry, of which 

 the following may be mentioned : 



(1) Stem form factors, which refer only to the volume of 



the stem above ground. 



(2) Tree form factors, which refer to stem and branches, 



omitting root wood. 



(9) Timber form factors, which refer only to those parts of 

 the tree which are classed as timber, whether they are 



