57 



deteremined either by weighment or by ascertaining the 

 volume.^ The solid contents are calculated by reducing 

 factors in the same way as the solid contents of small 

 wood. Experiments give from 0-3 to 0*4 as the average 

 factor for bark. It has been found that the quantity of 

 bark varies from 6 to 15 per cent, of the total volume 

 of the tree or crop. 



There is in India only one practicable method of arriving 

 at the contents of standing trees, namely by means of form- 

 factors. It has already been explained that the cubical 

 content of a tree is equal to some fraction {f) of the ideal 

 cylinder whose basal area is equal to the section of the tree 

 at breast-height and whose height is that of the stem. 



Form- factors may be deduced, according to the require- 

 ments of the case, for the whole tree, for the stem only, or 

 for the branches. 



It has been supposed that the sectional measurements 

 have been taken at the height of a man's chest, assumed, for 

 the sake of uniformity, to be 4 feet 6 inches above the 

 ground. But it is obvious that any other conventional 

 heiglit would serve the purpose, although it is usual and 

 most convenient to employ the one we have adopted. We 

 need refer to only one other convention which is sometimes 

 used. The diameter may be measured at a constant fraction 

 (say, for instance, one-twentieth) of the height of the tree, 

 in which case the form-factors obtained are termed normal. 

 Normal form-factors yield perfectly correct results; but they 

 are not practical owing to the difficulty and trouble of mea- 

 suring at various heights from the ground, Form-fictors are 

 said to be absolute when the base of the ideal cylinder is 

 assumed to be in the same horizontal plane as the diameter 

 or girth measured. In this case the contents of the 

 portion of the stem below the plane must be calculated 

 separately. 



As may be supposed, calculations based on form -factors 

 give better results for an entire forest than for individual trees. 

 The preparation of a complete set of form-factors requires 

 great care and experience, as ultimate accuracy depends 

 entirely on the selection of the type-trees whose dimensions 

 serve as the basis of all the calculations. In some cases the 

 trees of a crop have been groupedinto various classes accord- 

 ing to their height and shape, and a separate form-factor 

 calculated for each class. The most recent investigations 



