<St>i JOURNAL OF FORESTRY 



(|_T V 



— — hj- by its value D-, we get 



D'- = D=^ + D=2 = 2D^ 



Substituting this value of D'- in equation II, we get 



2 ;/'- D- 



n^ D- 



= /-; and simplifying 



~-~ = f-,orf = -\/2. 



11 



Since \/2= i .414, 



"' 

 f=^ X 1.4- 

 11 



TT 



When, therefore, D = — — /;, the coefficient of form of any given 



tree equals the quotient of the apparent diameter at the middle of the 

 trunk divided by the apparent diameter at the height of the observer's 

 eyes, multiplied by the constant 1.4/ 



The actual steps necessary to determine the coefficient of form of a 

 standing tree may be summarized as follows : 



a. Measure the height H of the trunk by eye or by one of the well- 

 known methods, and, once for all, the height h of the observer's eye 

 above the ground. 



b. Walk to a distance from the tree equal to half the height of the 

 trunk minus the height of the eye above the ground. Practical ex- 

 perience has proved that it is sufficient to walk to a distance from the 

 tree approximately equal to half the height of the trunk in order to 

 determine without appreciable error the apparent diameters n and n'.'' 



c. From this point determine the apparent diameters n and n on a 

 graduated scale held at arm's length and parallel to the line between the 

 eyes and directed successively at the height of the eyes on the tree and 

 at the middle height of the trunk. 



Let us suppose that for a given tree the observer, the height of whose 

 eyes above the ground equals i . 5 meters, finds that H = 9 meters. To 

 determine the coefficient of form / of this tree it is sufficient to walk to 



<: The same formula can evidently be used to determine the diameter at any 

 given point on the tree, provided one stands at a distance from the tree equal to 

 the height above the ground of the point at which the diameter is to be measured 

 minus the height of the observer's eyes above the ground. In this case /, instead 

 of being the ratio between the diameter at the middle height of the trunk and the 

 diameter at the height of the eyes, is the ratio between the diameter at the point 

 .'■elected and the diameter at the height of the eyes. — S. T. D. 



'i See comment h\ Mr. Sparhawk in regard to this point. — S. T. D. 



