336 



Mr. (Jr. F. C. Searle on the Steady Motion 



corresponds to an ellipsoidal equilibrium surface ; the other 

 to a hyperbolic surface whose lines of intersection with planes 

 passing through the axis of x are the lines of electric force. 

 The lines of electric force for a charged sphere in motion are 

 not radial but form a series of hyperbolas. 



Figs. 2 and 3 show the forms of the equilibrium surfaces 

 and of the lines of electric force, for a line and a disk respec- 



Fiff. 2. 



X=-4 



\-s 



/U3 



A=< 



*=-t 



X=< 



A--» 



A,=- 



A,= 





tively, when a = \ so that u/v = -866. In fig. 2 the curve 

 marked \ = | is a circle, a section of the sphere of which the 



