34 LOG RULES BASED ON CUBIC CONTENTS 



Two-thirds Rule. By this rule, the diameter of the log is reduced 

 one-third, the remainder squared, and multiplied by the length of the 

 log. As diameters are in inches the formula is V = (f-D) 2 L-4-144. 

 This is a caliper rule applied to the middle area, and gives 56.5 per 

 cent of the full cubic contents of the log. It is sometimes erroneously 

 applied to the small end. 



Quarter Girth or Hoppus Rule. This rule depends upon the direct 



use of the girth, rather than diameter. The average girth is taken 



(G\ 2 

 in inches at middle point, or by averaging both ends. Then V= I -I L. 



This formula gives 78.5 per cent of the actual total cubic contents of 

 the log. It is a commonly used standard for measuring round logs in 

 England and India. To express the contents in cubic feet the result 

 is divided by 144. 



36. Log Rules Expressed in Board Feet but Based Directly upon 

 Cubic Contents. The Blodgett or New Hampshire rule is not the only 

 log rule based on cubic contents, which attempted to express the results 

 in terms of board feet. Any cubic rule can be converted into board- 

 foot form, in theory, by the use of a ratio similar to those used for the 

 Blodgett Rule. The ratio for board-foot contents of one cubic foot is 12. 

 Twelve 1-inch boards cannot be sawed from 1 cubic foot, but a squared 

 timber 12 by 12 inches contains 12 board feet per linear foot. For con- 

 verting the entire log directly into board-foot contents of squared 

 timbers, it is evident that the ratio will be less than 12 board feet per 

 cubic foot, due to waste in squaring the log, while the conversion into 

 contents in inch lumber requires a still lower ratio. 



The characteristic of all converted rules is that a fixed multiple 

 or converting factor is used, regardless of the diameter or taper of 

 the log. The rules differ only in the converting factor used, and in 

 the method of measuring the log, whether at middle, or end. 

 , Constantine Log Rule. This rule is merely the expression of the cubic 

 contents of a log regarded as a cylinder, in terms of board feet, by 

 multiplying the cubic contents by 12. The diameter is measured at 

 the small end of log. The formula is 



4X144 



The rule is used to measure the contents of logs used for veneers. 



Cuban One-fifth Rule. This Rule is based on the square of one- 

 fifth of the girth taken in middle of log. The formula when G is in 

 inches is 



-©'** 



12. 



