THE CONTENTS OF LOGS AND TREES 179 



The height of a tree can also be found by the use of two 

 staffs. The observer moves away from the tree about 50 to 

 75 feet until he can see the top and base of the tree. A staff 

 6 to 8 feet high is then set upright at this point (.v in dia- 

 gram). A few feet farther away from the tree a second staff 

 about 4 feet in height is set at (3;). The observer now looks 

 from the top of the staff (3;) at A across the first upright 

 staff (.r) to the top of the tree (B ) and an assistant marks 

 on the staff (,v) the point (D) where this line crosses. The 

 observer now looks from (A) to the bottom of the tree and 

 the assistant marks on the staff (.r) the point () where this 

 line crosses. 



The distance AC or from the eye of the observer to the 

 foot of the tree multiplied by DE the length marked on the 

 staff (,r) and this product divided by AE, the distance from 

 the eye of the observer to the staff (.r), will give the height 

 of the tree. 



, 4 vr ACXDE 



Height of tree : BC = . 



(For AC the distance yc on the ground can be measured, 

 and for AE the distance y.v on the ground can be measured.) 



