The time-independent Hamilton-Jacobi equation is separated in parabolic coordinates to solve the problem (in principle) of the motion of a non-relativistic electron in a Coulomb potential in the presence of a constant external electric field, the so-called Stark effect. The separability of the H-J equation in these coordinates was discovered by Jacobi, and the application to the linear Stark effect was first achieved by Karl Schwarzschild, of the Black Hole solution fame!