THE MEASUREMENT OF TIMBER. 1 33 



2. The Custom House quarter-girth rule has also been 

 referred to. The formula in this case is : — 



V = 



(5)'" 



"3 



Practically the true contents of a cylindrical log can be obtained 

 from this rule. The method of arriving at the result, however, 

 is unsatisfactory. It is obviously simply a method of correcting 

 the result obtained by Hoppus without altering the erroneous 

 system of measuring. Neither of these two systems gives a 

 true sectional area, and both, for that reason alone, are useless 

 for scientific work. 



3. Fifth girth is a very old rule, which is said to be still used 

 in France, and was at one time in use in Britain. The formula 

 for this rule is : — 



V -5 



144 



Twice the fifth of the girth in inches squared, multiplied by 

 the length in feet, and divided by 144 to obtain cubic feet. 

 The rule is very much more accurate than the quarter-girth 

 rule, and gives a sectional area approximately correct as the 

 following example shows : — 



Take a circle 40 inches in circumference. The area by fifth 

 girth rule — 



= 2 (m\ ' = 2(8) 2 = 1 28 sq. inches 



or -888 sq. feet 

 the actual area being -883 sq. feet. 



This rule, however, has the fault common to all rules necessi- 

 tating the girth measurement, i.e. that it can only be applied 

 if the section of the log is a perfect circle. 



4. Newton's rule. — For this rule the following measurements 

 are required, viz. length, sectional area at butt, middle and 

 tip of log. 



V=(A b + 4 A m + A t )^ 

 o 



This formula holds good for obtaining the volume of a truncated 

 cone, paraboloid or neiloid, and is extremely accurate. It, 

 however, necessitates a considerable amount of measuring, 



