RULES AND MEASURES. 



221 



of its shadow as the height of a pole is to the length of its 

 shadow. 



A more general method is to set up two poles in line 

 with the tree. From some point, P, in the farther pole 

 (as the top) sight across the second pole to the base, A, 

 of the tree and mark the point C, in which this line cuts 

 the second pole. Do the same for the top of the tree, 

 thus determining the point D. Then measure the dis- 

 tances, P A, P C, and C D. Now the height of the tree 



B 



r 



USING POLES TO GET HEIGHT OF TREE. 



is in the same ratio to the distance P A as the distance 

 C D is to the distance P C. Therefore, the height of the 

 tree, 



CDXPA 



A B = 



PC 



This method may be used to determine the vertical dis- 

 tance between any two points on the trunk of a tree by 

 finding the difference of their distance from the base. 



