12 



INSTRT'MKNTS USED IN MENSURATION. 



ill practice, because those at present available either do not 

 Mork \Yith sufficient accuracy, or take too much time. 



3. Instruments for tlie Measurement of the Diameter Inerement. 



The diameter increment of prepared sections is measured 

 with an ordinar}- rule, or with a pair of compasses and a rule. 

 Such rules are made of metal or wood, and are sufficiently 

 sub-divided. 



If no section is available, as in the case of standing trees, 

 the measurements are made with Pressler's Increment Borer 

 (Fig. 6). This instrument extracts a cylinder of wood from 

 the stem, and it consists of the following parts : — 



(a.) A hollow borer, A, which is slightly conical from the 



handle towards the point. 

 (b.) A handle, B, which serves as a lever when the instru- 

 ment is in use. It is hollow and serves to receive the 

 borer, wedge and cradle, when the instrument is not in 

 use (see E in figure), 

 (c.) A wedge, C, which has a scale marked on one side 

 wherewith to measure the breadth of the concentric 



