236 



THE MEASUREMENT OF STANDING TREES 



b/' 



height equal and whose line of sight from eye to top coincides with that 

 from eye to tip of tree gives this result. 



A straight stick or short pole may be grasped by the thumb and first 

 finger at a distance from its top exactly equal to the distance from the 

 eye to the point thus marked. Holding this stick vertically, which 

 is best accomplished by having the greatest weight below the hand 

 to act as a pendulum, the observer moves backward or forward until 

 the line of sight Ab in Fig. 43 cuts the desired upper point on the tree, 

 and at the same time the line of sight Ac cuts the tree at its base. At 

 this point the triangle Abe has become similar to the triangle ABC, 

 and AC is equal to BC. The measured distance from eye to base of 



tree is then equal to the 

 height of the tree. This 

 distance can be measured 

 along the ground to the 

 point below the eye with 

 sufficient accuracy, pro- 

 vided the slope is even. 

 Thismeasurementof height 

 can be taken from any 

 point of elevation, either 

 on a level with, above, 

 or below the base of the 

 tree without affecting its 

 accuracy. 



195. The Principle of 

 the Klaussner Hypsom- 

 eter. For height meas- 

 urements which require 

 greater accuracy than is obtainable by such ocular methods as the 

 one just described, the small triangle is constructed in the form 

 of an instrument called a hypsometer, on which two of the sides 

 corresponding respectively to the lines AC and BC, or distance 

 to tree and height of tree, are graduated to units of distance. This 

 enables the observer to first adjust the scale AC for distance, 

 to equal in feet the known distance from the tree, hence to determine 

 what this distance shall be. The line of sight from the eye, beginning 

 at the zero point of this scale or apex of the small triangle is now brought 

 into line with the point on the tree whose height is to be measured, 

 which makes the small and large triangles similar. The point at which 

 this line of sight cuts the scale BC, whose graduations are equal to those 

 on the scale AC indicates the height of the tree. These graduations 

 may be of any size so long as both scales are graduated equally. They 



— ""•• M *v™«, < 



Fig. 



43. — Similar isosceles triangles formed by use 

 of pole, for measuring height of trees. 



