Solitons

Introductory lecture given at the Chalmers Symposium on Solitons, Göteburg, June 1978 I will briefly discuss a few topics in soliton physics which have recently been considered. I first of all deal with some aspects of the relation between the Zakharov equations and the non-linear Schrödinger equation in the small Mach number regime, focussing attention on the adiabatic invariants and their relation to conservation laws. I secondly describe some experimental results about non-linear deep-water waves, and I end with a brief discussion of some aspects of spiral density-wave theory.