Perturbation Theory in Wave Mechanics

This note is intended to supplement a recent article by Speisman by focusing attention on some points of a rather practical nature. In particular, it is shown that the method of Dalgarno and Lewis arises naturally as a special case of the present scheme, and that an upper bound to the energy can be obtained almost immediately once the results of the Rayleigh-Schrödinger theory are known to third order.