134 ELEMENTARY FORESTRY. 



mately the same dimensions and grown under the same condi- 

 tions. The form factor is expressed as a decimal, and is the ratio 

 of the mean volume of the sample trees to the volume of a cylin- 

 der with the same diameter as the diameter of the mean sample 

 tree at breast height, and whose length is equal to the height of 

 the tree. For example: A tamarack measures 6.9 inches in diam- 

 eter, breast high, and the height of the tree is fifty-one teet. Its 

 volume by accurate measurement of the felled tree is 7.21 cubic 

 feet, and the volume of a cylinder with a diameter of 6.9 inches 

 and a length of fifty-one feet is 13.24 cubic feet. The form 

 factor, or factor of shape, is therefore 7.21-^13.24=3.54, and if 

 this tamarack represents the mean of a large number of trees 

 of approximately the same dimensions, the factor may be applied 

 to all of them, or to all trees of the same size and grown under 

 the same conditions. In the same way factors are determined 



Figure 37. Determining the volume of a felled tree. 



for all sizes, and tabulated for future use. In application the 

 volume of a tree 6.9 inches in diameter, breast high, and fifty- 

 one feet high would be found thus: Volume of cylinder X form 

 factor equals volume of tree, or i3.24X-54=7-2i. This method 

 gives a much closer approximation than could be obtained by 

 using a geometric figure supposed to represent the shape of the 

 tree. 



The Volume of a Felled Tree may be determined more 

 accurately. It is considered in sections, or log lengths, and the 

 volume of each section is found by multiplying the middle cross- 

 sectional area by the length. The degree of accuracy of this 

 method depends on the length of the sections; the shorter they 

 are the more accurate the result. The last section at the top, 

 when small, may be treated as a cone whose volume is equal to 

 the basal area times one-third its length; or when large and 

 tapering off suddenly it may be considered as a paraboloid whose 

 volume is equal to the basal area times one-half its length. The 



