MEASUREMENT OF TIMBER 191 



whereas its true volume would be : 



8 x 8 x 0-0796 x 30 = loi-S cubic feet. 



If the quarter-girth is taken in inches and the length in feet, 

 then the result must be divided by 144. 



Thus if a log has a girth of 3 feet 4 inches and length 

 20 feet, its quarter-girth will be 10 inches and its volume: 



IOX IOX 20 . 



- = j<? feet 10 inches, 

 144 



an inch being T \th part of a cubic foot, and not a cubic inch, 

 which is -i^Vsth part of a cubic foot. An inch in timber 

 measurement is therefore a block of timber equal to 144 cubic 

 inches. 



The true cubic contents can also be obtained approximately 

 by this method, dividing by 113 instead of by 144, thus the 

 true contents of this log will be : 



IOX IOX 2O . r 



= 17-7 cubic feet. 



H3 



A woodman who does not happen to be well acquainted 

 with arithmetic will find this method to be the easiest one 

 with which to work out the true volume of any log. It is 

 sometimes used in England by railway companies to calculate 

 the volume of logs upon which carriage charges are paid. 

 True measure should be used in all measurements taken for 

 scientific purposes. 



It is sometimes useful to be able to turn true measure into 

 quarter-girth measure rapidly. To do this deduct 21^ per cent, 

 from the true volume. Thus a log which is 200 cubic feet by 

 true measure will be 200 (21 \ per cent, of sco) = 200 43 = 

 157 cubic feet by quarter-girth measure over bark. To make 

 a bark allowance deduct 16 per cent, of this, thus volume by 

 quarter-girth measure under bark is 157 (16 per cent, of 157) 

 = j^ s^ =132 cubic feet. In the same way the true volume 

 of a log over bark is obtained from the volume by quarter- 

 girth under bark, by adding 53 per cent. ; thus a log whose 



