13 



half of that at breast height (D); this point is called the guide point. 

 This iDoiut can be determined by estimate after some practice or else 

 by use of a simple iustrument (fig. 7) consisting of three hollow cylin- 

 ders (A, B, and C), which fit one into the other. 

 The instrument then can be lengthened and 

 shortened in the same way as an ordinary tele- 

 scope. The cylinders may be made of stiff ma- 

 nila or other similar paper. Into the outer 

 cylinder (A) two pins {Ic and I) are thrust 1 inch 

 from the end; they can be moved in and out, 

 permitting a change of distance between their 

 heads. Cylinders A and B are of the same 

 length, 13 inches each, while that of is 2 inches 

 long. The end of cylinder is closed by a 

 paper cover, in the center of which a hole {y), 

 of one-fourth inch in diameter, is made as an 

 eyepiece. Looking through the eyepiece (?/), 

 arrange the heads of the pins so that the dis- 

 tance between them coincides exactly with the 

 diameter of the tree at breast height. With- 

 out changing the distance between the heads 

 of the inns, the observer draws out the cylin- 

 ders so as to double the former length, allowing 

 for that purpose the two inside cylinders to 

 project into each other 1 inch; then range the 

 telescope up the trunk until a point is found 

 where the diameter of the tree again corre 

 sponds with the distance between the heads of 

 the pins. At this point the diameter of the tree 

 is one-half of that at breast height. To obtain 

 the volume of the tree, estimate or measure the 

 height of the guide i)oint, add 2 feet, and multiply this sum by two-thirds 

 of the area corresponding to the diameter (D) measured at breast height. 

 Example: A tree of 2Q inches in diameter at breast height is 13 



Fig. 6.— P^e^ssler's met hod of 

 determining the volume of a 

 standing tree. 



[<-C~N 



4-*]\c]. 



Cylinders closed. 



HI 



Cylinders drawn out. 



Fig. 7.— Instrument used for determining the guide point. 



K 



D 



I 



inches in diameter at a height of 60 feet from the ground — that is to 

 say, the height of the tree to the guide point equals 60 feet. Adding 2 

 to 60 and multiplying by two-thirds of 3.69 (3.69 square feet represents 



