FOREST MANAGEMENT 119 



of the stem cross it at b and a. The ray DC is horizontal. 

 Taking the measurement of the distances from the observer 



FIG. 25 



to the staff and to the tree, the height can be obtained by the 

 formula 



TT ba x DC 



Faustmann's Hypsometer, or height measurer, is shown in 

 Fig. 26. With it a tree's height can be ascertained from 

 any convenient position from the stem, provided one can see 

 from it both the top and the base of the tree. The distance 

 from the observer to the base of the tree is measured, and the 

 vertical scale (g, e) is adjusted accordingly. Then, sighting 

 through a and b to the tree top, the pendulum (S), with the 

 plumb-line resting on the horizontal scale, gives the height 

 plus or minus the difference in level between the eye of the 

 observer and the foot of the tree. This latter point is 

 quickly decided by sighting to the tree's base, and adding or 

 subtracting according as the result indicates. 



