TWO LINES OF OPPOSITE SIGNS. 



117 



When all the masses are of the same sign, all the lines of force 

 are unlimited. In the contrary case, part of the flow of force 

 issuing from positive masses is absorbed by negative masses. 



From the method of numbering adopted, the number of un- 

 limited lines of force is equal to the difference between the number 

 of positive lines and of negative lines. 



If the electrified lines A, A', A" . . . . , while still parallel, are no 

 longer in the same plane, the construction of lines of force becomes 

 more complicated. In this case, the value of the potential at a point 

 P at distances r, r\ r" . . . from the lines A, A', A" ---- , is 



V = const - % 2 XI. r = const - 2/. (r 



whence 



const 



135. Two LINES OF OPPOSITE SIGNS. Consider the particular 

 case of two lines electrified oppositely, defined by the masses +m 



Fig. 29. 



and - m', situate at two points A and A' (Fig. 29) at the distance 20, 

 and let m be the greater of these masses. The equation of a line of 

 force becomes 



from which 



n ri = N, 



mat m'w = mO ; 



