190 FELLING AND 



on a section cut in the middle of the log. This may be found 

 from the girth by the formula : 



Sectional area = (girth) 2 x 0-0796 



the expression (girth) 2 being read as 'girth squared', and 

 meaning girth multiplied by girth. 



The volume is therefore : 



(girth) 2 x 0-0796 x length. 



Thus if a log has a girth in the middle of 6 feet, and is 

 20 feet long, the volume is 



6 x 6 x 0-0796 x 20 = 57-31 cubic feet. 



To make the working-out of the sum shorter one can use 

 the figure 0-08 instead of 0-0796, in which case the cubic con- 

 tents of the above log would come to 



6 x 6 x 0-08 x 20 = 57-6 cubic feet. 



If the diameter in the middle of the log is measured with 

 callipers, the sectional area is found by the formula : 



Sectional area = (diameter) 2 x 0-7 85, and the volume is there- 

 fore : (diameter) 2 x 0-785 x length. 



Thus if a log has a diameter in the middle of 2 feet and 

 length 20 feet, its volume will be : 



2 x 2 x 0-785 x 20 = 62-8 cubic feet. 



The above methods give the true cubic contents of the log, 

 but the woodman will hardly ever be called upon to make 

 these calculations in England, as timber is measured here by 

 a system called the sqtiare-of-quarter-girth measurement, 

 which makes an allowance of 21^ per cent, for wastage in 

 conversion. By this system the volume is found by the 

 formula : 



Volume = (^ lrth /x length. 



Thus if a log has a girth of 8 feet and length 20 feet, its 

 volume is : 



f x | x 20 = 2 x 2 x 20 = 80 cubic feet, 



