Roever — Geometrical Constructions of Lines of Force. 215 



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

 with AO is by equation (8), 



m — m m 



a a — 7T = 7T 7T, 



m nt 



Fig. 6. 



Tit 

 in which — rr is the ans;le between the two tangents, at A, 

 m 



to a loop. 



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

 equation of the form * 



7iMo + m'to = 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. 



* If oj can have values ranging only from a to d, equation (2) accounts 

 only for the 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. 



