of ascertaining the Heights of Trees. 



519 



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the diameter of the tree, or the liney^. This is an operation 

 which we have seen an expert practitioner perform in two minutes; 

 but we may allow, at an average, ten minutes to each tree. 



The height of single trees may also be taken with expedition 

 during bright sunshine by their shadows. Set up a rod, say of 

 6 ft. in height above the surface, and measure its shadow ; then 

 measure the tree's shadow, and find the height by the Rule of 

 Three. 



For both the last modes the tree must stand on level ground, 

 otherwise additional observations must be taken, which it would 

 occupy too much space to explain here. The reader will find 

 this done in an excellent paper by Mr. Gorrie, on measuring 

 trees, in Vol. II. p. 8. When single trees are on a sloping bank, 

 their height may be taken by the square, by looking at them 

 across the slope, that is, by looking at them on a horizontal plane. 

 By rods, of course, their height may always be taken in what- 

 ever way they are situated. 



The diameter of the trunk of a tree may be readily taken by 

 girting the tree with a string, one third of the length of which 

 will give the diameter ; or the tree may be measured with a rod, 

 having a piece fixed to it at right angles at one end, and a sliding 



p p 4) 



