16 

 and 



Again, 

 and 



Hence, 



INSTRUMENTS USED IN MENSURATION. 

 be x D G 



A G :ac = D C : DC 



A r _ ac x D G 

 ~D~e 



BC+AC=AB= height of tree = ft <* + _a c) x 7? 



Fig. 8. 



(2) The horizontal plane passes below the foot of the tree. 

 In that case (Fig. 8) : 



DC 



(3) The horizontal plane passes above the top of the tree 

 (Fig. 9). Then : 



H = AC-BC = i a 



In each of the above three cases two measurements are 



