CHAPTER III. MENSURATION AND INCREMENT. 



9. The quarter-girth convention. 



THE cubic contents of a log of wood are found by multiplying 

 the sectional area at the middle of the log, which presumably 

 tapers, more or less evenly, from one end to the other, by its 

 length. In terms of the girth at the point where the sectional 



2 

 area is taken, this area equals J - . 



4.7T 



The volume in cubic feet therefore, if the girth is measured in 

 inches and the length in feet, will be 



2 I 



- x length. 

 4.77 144 



This will give the true volume. 



For commercial purposes, however, the true contents are not 



calculated, but instead, the quarter-girth measure is employed. 



/>\i 

 In this method the sectional area is taken ( -) , or, in other 



V 



words, TT is taken as 4. 

 Therefore, 



the quartej-^rth volume _ 3*14159 _ 78-5 _ 113 

 the true volume 4 100 144 ' 



and the true volume can be obtained from the quarter-girth 

 measure by dividing by 113 instead of by 144. 



Thus the ordinary Custom-house formula, by which import 

 duty is levied on foreign timber, is 



(j x length 



-2 - = true cubic feet. 



whereas the ordinary commercial Hoppus measure, which is 

 78J per cent, of the real contents, is 



x length 

 144 



