Roever — Geometrical Constructions of Lilies of Force. 22 1 



wi = 4 and — m' = — 1, respectively; and Fig. 9 shows a few 

 of the lines of force proceeding from a system consisting of 



two electrified points A and A' having charges wi 

 W2' = 1 respectively. 



If 7n = m, numerically, equation (24) becomes 



= 4 and 



or 



(1 — cos co) — (1 — oos Q)') = 1 — COS a 



cos co' — cos ft) = 1 — cos a ( 28) . 



This is the equation of a closed curve passing through A 

 and A'. A line of force is only an arc of this curve. 



If ft) = Q)' = 6, then, from equation (24), 



versin 6 = 1 — cos 6 = 



m 



m — 711 



-, (1 —cos a).. (29). 



This determines the direction of the asymptote to a line of 

 force. 



