292 Trans. Acad. Sci. of St. Louis. 



For a = equation (26) becomes 



m versin co = irax^ (38)' 



This result is also obtained by making a^o = in equation 

 (27). This is the equation of the limiting or critical line. 

 This line is the meridian curve of the surface of revolution 

 which separates the lines of force terminating in the elec- 

 trified point from those which never reach it. The dashed 

 line in Fig. 6 is the critical line. For the point / in which 



the critical line cuts 01% — = 27r<T or 



TT 



= '•« = ^l^. («»)• 



«^ 2.. 



Inspection shows that (26) is the equation of a line of 

 force which is inside the critical line and (27) is the equation 

 of a line of force which is outside the critical line. 



For a) = TT equation ( 26) becomes 



m (2 — versin a) 



^'=— :;^ (40)» 



TTff 



in which x^ is the distance from to the asymptote of a line 

 of force which is inside the critical line. For to = tt equa- 

 tion (27) becomes 



in which (cc^, — jc^) is the distance between the two parallel 

 asymptotes to a line of force which is outside the critical 

 line. 



For a = equation (40) becomes 



/2m 

 ^^ = VW = 2-0 (42), 



which is also obtained by making Xq = in equation (41). 



