Boever — Geometrical Constructions of Lines of Force. 215 



The angle which a tangent, at A to the limiting line, makes 

 with -40 is by equation (8), 



m — m m 



a. = TT = TT . TT, 



m in 



in which — tt is the angle between the two tangents, at -4, 

 m 



to a loop. 



In Fig. 3 is shown the complete curve represented by an 

 equation of the form * 



ma) + m'(o' = ma (2). 



The parts are traced in the order indicated by the num- 

 bers. Parts 4 and 5 form a branch which passes through A' , 

 the remaining parts form branches which pass through A. 



* Jt (o can have values ranging only from a to 0, equation (2) accounts 

 only for tlie lines of force that proceed from the charge m. In order to ac- 

 count for the lines of force that proceed from charge m' we must interchange 

 m and m' in equation (2) and count angles in the opposite direction. 



