6 spheres with the + and - regions of Lam
G. Lamé solved Laplace's equation $\Delta\phi=0$ by separation of variables in elliptic coordinates; this led him to study transcendental functions called Lamé functions, and defined by a second-order ordinary differential equation. Three solutions are shown here, by drawing on the Riemann sphere the sign of the real part of the function.
Courant-Hilbert. Methoden der Mathematischen Physik, Bd. I, 5. Chap. §9.