This sub-series consists of 11 files relating to Edward Appleton's work on oscillators. This was one of his earliest research interests, developed from his work on the thermionic valve during and after the First World War, and he later pursued in collaboration with B. van der Pol (see Coll-37/E.117-E.144). Virtually none of this material is dated. Appleton's own notes and drafts, which appear at Coll-37/C.237-C.240 would seem to date from the 1920s. The correspondence and data, which appear at Coll-37/C.241-C.247, show the continuation of research on non-linear oscillations by Appleton's students at King's College, London, and include exchanges with M.L. Cartwright and J.E. Littlewood on mathematical aspects of similar problems in the 1940s.