WRIGHT: SOLUTION OF EQUATION A=B-C 



In case A, B, C are functions of variables the equation 

 A = BC may be considered to express relations between the 

 functions themselves, namely, between A, B, and C rather than 

 between the variables; fundamentally, of course, the equation 

 expresses relations between the variables, and the increments 

 are so taken. The procedure adopted below amounts practically 

 to the representation of each function by a scale so chosen that 

 the resulting curves are straight lines. Straight lines can be 



Fie.l 



A 



B 



A. B. C < 1 



<^^ 



Fig.2 



Fig.3 



Fig.4 



A, B <1. C>1 A. B >1. C <1 



Figs. 1 to 4. Diagrams for graphical solution of certain equations. 



drawn more readily and more accurately than curves; straight 

 line diagrams are, moreover, easier to read. In the paper cited 

 above a number of straight line diagrams are included which 

 serve for the graphical solution of the equations encountered in 

 microscopical petrography. These diagrams have been found in 

 practice to be useful and time saving. 



Recently a device has been adopted by means of which these 

 equations and others of the same general form can be solved with- 

 out requiring a special plot for each type of equation. Its con- 



