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INSTRUMENTS FOR MEASURING HEIGHTS. 



There are several methods of determining the height of a stand- 

 ing tree. One of the simplest is to measure the shadow of the tree 

 and the shadow of a straight pole of known length set perpendicular 

 to the earth. Multiply the length of the shadow of the tree by the 

 length of the pole and divide the product by the length of the 

 shadow of the pole. The result will be the height of the tree. 



A method used when the sun is not shining is to set two poles 

 in a line with the tree. (See fig. 6.) From a point on one pole 

 sight across the second pole to the base and to the top of the tree. 

 Let an assistant note the points where the lines of vision cross the 

 second pole and measure the distance between these points. Also 



FIG. 7. Measuring the height of a tree by use of known height to eye of the observer. 



measure the distances from the sighting point on the first pole to 

 the base of the tree and to the lowest vision point on the second 

 pole. Multiply the distance between the upper and lower vision 

 points on the second pole by the longer of the other two measure- 

 ments and divide by the shorter; the result will be the height of 

 the tree. 



Example: Let a&=6; 6=4; and S#=30; then = 45, height 



of tree. 



Another method sometimes used is as follows: The observer 

 walks to a distance from the foot of the tree about equal to its 

 estimated height. He then lies on his back, stretched at full 

 length (fig. 7), and an assistant notes on a vertical staff erected 



