CHAPTER I. 



INSTRUMENTS USED IN FOREST MENSURATION. 



INSTRUMENTS are required to measure the circumference or 

 diameter of logs and trees, the length of logs, the height of 

 trees, and the increment. Such measurements have for 

 their object, either to ascertain the various dimensions, or to 

 calculate from them the volume ; in the latter case the measure- 

 ment of the girth or diameter is used to calculate the sectional 

 area, on the assumption that it forms a circle. 



The instruments may be classified as follows : 



t 

 1. Instruments for the Measurement of the Girth. 



The girth may be measured with a tape, or with a string 

 and tape. 



The tape consists of a band, of about half an inch in breadth, 

 so constructed that it alters its length as little as possible when 

 moist. It is divided on one side into feet, inches, and, if 

 necessary, decimals of inches ; on the other side the sectional 

 areas corresponding to the length of girth are sometimes noted. 

 It is useful to have a small hook on one end, which can be 

 pressed into the bark when the girth exceeds 5 feet. Long 

 tapes are rolled up in cases, which are made of leather, wood 

 or metal. 



Of late years flexible steel tapes have come much into use. 



The advantages of the tape are, that it is easy to handle and 

 convenient to carry. 



Measurements with the tape are subject to various sources 



