7'83 



TOURXAL OF FORESTRY 



When .r = i i.^ .r - + i ^ i . 5 



= 2 =3 



= 3 =5-5 



= 4 = 9, etc. 



The graduations i, 2, 3, 4, etc.. are then placed at 1.5, 3. 5.5. 9, etc., 

 units from the origin. 



COMBINATION OF OPERATIONS 



Many formulae involve the addition or multiplication of more than 

 two variables or both an addition and a multiplication. Such cases are 



-Z 



-/ 



B 



-2 



-/ 



CL lA- 



-S 



-4- 

 -3 

 -2 

 -/ 



FiG. 7. — Elenientarj' chart for addition of three terms. 



simply provided for by constructing two systems of axes in which the 

 final axis of the first system becomes one of the initial axes of the 

 second. The method will be evident from a consideration of figure 7, 

 designed to solve the equation v = x + 3' + ^. 



The first system consists of the lines A, B, and C, x being measured 

 on A and r on C, so that the final axis B will measure the sum x -f- T- 

 This B axis then becomes one of the initial axes of the BDE system. If 



