CUBIC MEASURE. 53 
CUBIC CONTENTS OF SQUARE TIMBER IN ROUND 
LOGS. 
The most common methods of determining the cubic contents 
of square timber that may be cut from round logs is the so-called 
Two-thirds Rule, and the Inscribed Square Rule. 
The Two-thirds Rule. 
In the Two-thirds Rule the diameter of the log is taken at its 
middle point, or the diameters of the two ends of the log are aver- 
aged. The diameter of the log is reduced one-third to allow for 
§ slab and the remaining two-thirds is taken as the width of the 
square piece which may be hewed or sawed out of the log. The 
cubic contents of the squared log are then obtained by squaring 
this width and multiplying by the length of the log. 
This rule gives smaller results than the Inscribed Square Rule, 
which shows the contents of a square piece that may be exactly 
inscribed in a cylinder of the same diameter as the log. In sup- 
port of the Two-thirds Rule it is claimed that there is a certain 
amount of waste, due to the fact that logs are seldom perfectly 
round and eae and that the rule makes approximately the 
correct ioe eee for such irregularities. 
The Two-thirds Rule is sometimes called the Big Sandy Cube 
Rule. : 
| _ The Inscribed Square Rule. 
The Inscribed Square Rule gives the cubic contents of square 
pieces which can be exactly inscribed in cylinders of different 
sizes. The width of this square piece is usually obtained by mul- 
} tiplying the diameter of the cylinder by 17 and dividing the result 
by 24, or by multiplying the diameter by 0.7071. This rule of 
1 | Saumb for calculating the width of the inscribed square piece is 
)) based on the fact that one side of the square inscribed in a circle 
))| 24 inches in diameter is 17 inches long. 
The exact mathematical rule for determining the side of a square 
} inscribed in a circle is to square the diameter, divide-by 2, and 
| -extract the square root. The table following was computed by 
(| this method. 
| Practically the same results are obtained by the Seventeen-inch 
Rule, which is based on the fact that a 17-inch log will square 12 
| Reaches. According to the Seventeen-inch Rule ae cubic contents 
ofa log are ed as follows: Multiply the square of the diameter 
“of a log by its length and divide by the square of 17. 
