220 FORESTRY AND TIMBER 



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 

 \Ni(lth of this square piece is usually obtained by multiplying the diam- 

 eter of the cylinder by 17 and dividing the result by 24, or by multi- 

 jiiying the diameter by 0.7071. This rule of thumb 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 scjuare root. The table on the preceding page 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 inches. 

 According to the Seventeen-inch Rule, the cubic contents of a log are 

 obtained as follows: Multiply the square of the diameter of the log 

 by its length, and divide by the square of 17. 



