158 FORESTRY WORK 



2 per cent, deducted from the total. For example, as 

 above, 14xl4x0-8=166-8- deduct 2 per ceiit.=156.8 

 -S-0=153-8. 



To convert square of ^ girth figures to true con- 

 tents, multiply by 100 and divide by 78-6. (42.0x100) 

 -i-78-6=53 feet 5 inches. 



To convert true contents to square of J girth, multiply 

 by 78-6 and divide by 100. 



(53 feet 5 inches x 78-6) -*-l 00=42 feet. 



For girthing, special tapes are made showing the 

 I girth on one side in inches and quarters of an inch, and 

 on the other side the contents of 1 lineal foot of tree for 

 each J girth. For instance, 1 lineal foot of 11 inches 

 J girth contains feet 10 inches 1 part. Ail that is 

 necessary to find the contents of the whole tree is to 

 measure this figure by the length. 10 inches 1 part= 

 10^1^X50=42 feet inches 2 parts. 



A table at the end of the book gives the area of each 

 I girth, and by reference to this it is found that the area 

 of a square 11 inches on the side is '840 square foot. This 

 multiplied by 50=42*000 square feet. 



Instead of measuring the girth at the centre, it may be 

 taken at each end, the figures added together and divided 

 by 2, giving the mean girth. For example, 16 inches 

 I girth at the butt plus 6 inches | girth at the top = 22, 

 divided by 2, gives 11 inches as mean J girth. 



The I girth may be taken at many places on an irregu- 

 larly shaped tree, and the sum of all the ^ girths divided 

 by their number gives the mean |- girth. 



