11 



Fig. 4.— Calipers for raeasnring the diameter of 

 trees. 



In using the instrument the observer should select a spot from which 

 the top of the tree is distinctly seen; then measuring off the distance 

 from the tree in feet, shift the sliding scale until its lower end stands 

 opposite this distance. Thereupon sight from the eyepiece past the 

 hair line and the top of the tree and 

 read off in the mirror the figure 

 which the plumb line strikes on the 

 scale. In the same manner sight the 

 base of the tree and find the corre- 

 spondiug figure. The sum of the 

 two figures represents the height of 

 the tree when the observer is situ- 

 ated above the level of the base of 

 the tree. When the observer is sit- 

 uated below the level of the base of 



the tree the difference between those figures should be taken in order 

 to obtain the height of the tree. The figure represents the position of 

 the instrument when in use, the observer being supposed as on the 

 same level with the base of the tree and as shown on the sliding scale 

 at 100 feet distant; the height of the tree, as indicated by the position 

 of the plumb line reflected in the mirror, is 40 feet. When the in- 

 strument is not in use ail its parts 

 are easily folded and put into a case, 

 which can be conveniently kept in the 

 pocket. 



MEASUREMENT OF DIAMETER. 



The diameter of a standing tree is 

 usually taken breast-high or above the 

 swelling of the base and measured by 

 a pair of calipers, the essential parts of 

 which are a graduated rule, divided in 

 inches and subdivisions, with two arms 

 (fig. 4), one of which (AC) is fixed at 

 right angles to the graduated rule (AB), 

 while the other may be shifted along 

 the rule, remaining parallel to the im- 

 movable arm (AO). 



In measuring, the calipers are usually 

 placed breast-high horizontally against 

 the trunk, so that both the rule and 

 the immovable arm touch it; then the 

 movable arm is shifted along the rule until it is brought in touch 

 with the trunk, when the diameter can be read off on the rule. The 

 length of the rule depends upon the size of the trees to be meas- 

 ured, and the length of the arms should not be less than half of that 



Fig. 5.— Section of the movable arm of 

 Heyer's calipers. 



