# Page:SearleEllipsoid.djvu/8

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 respectively, when $\alpha=\tfrac{1}{4}$ so that $u / v = .866$.
In fig. 2 the curve marked $\lambda=\tfrac{4}{3}$ is a circle, a section of the sphere of which the