ABSTRACT
This chapter gives a very brief review of some methods for describing motions in a planetary system, including the perturbations which arise from their mutual gravitational attractions, and for deriving expressions of these in the form of asymptotic multiple Fourier series. It is shown how, with an appropriate choice of parameters to describe the orbits, these expressions contain only periodic terms, some however of very long periods (in the solar system, some of many millions of years).
