ii6 FORESTRY 



or divergent systems of treatment often makes it advisable to 

 fix different felling ages (rotations), and each of these necessi- 

 tates a working section. 



Measurement of Felled and Standing Trees, 

 and Determination of Increment 



Instruments used. A large number of instruments have 

 been devised to aid the forester in taking the measurement of 

 trees. A few of these must be described and their utility 

 explained. 



The Calliper (Fig. 21) is employed to find the diameter 



FIG. 21. CALLIPER 



r. Rule. 

 m. Movable arm. 

 f. Fixed arm. 



of the stem. It is constructed in a variety of forms, and has 

 long been in use for many purposes. In forest mensuration 

 callipers are of greatest value, though as yet they have found 

 little favour in Britain, chiefly because ocular measurements 

 and rough approximate estimates have been very generally 

 considered to be sufficient. The instrument consists of a 

 rule having a scale upon it graduated conveniently in inches 



