202 THEORY OF NEWTONIAN FORCES. [PT. I. CH. IV. 



In like manner if we have diagrams of the flux-function of 

 Q any two systems superposed, we may draw 

 diagrams of the flux-function of the sum or 

 difference of the two systems, for if we con- 

 sider two flux tubes bounded by the lines 

 AB, CD, and A'K, C'D', Fig. 48, the line PQ 

 has the flux A//, through it in opposite direc- 

 tions from the two systems, so that the total 

 flux through it is zero, or it is a flux-line. 

 In this manner the Figures 49*, 72, 74, 75, 76, 

 77, 78 have been drawn. 

 FIG. 48. 



Fm. 49. 



* Fig. 49 is to be considered a diagram of lines of flow or of equipotentials 

 according as the directions of the component vectors at the origin are the same 

 or opposite. The analogous cases of the rotational problem are represented in 

 Figs. 74, 75. 



