This series consists of 69 files and the material in it is entirely manuscript. It was prepared under Appleton's instructions by collaborators, students and assistants, mainly during 1949-1965, for various research projects on the ionosphere. Some of the charts are in identifiable hands such as those of A.J. Lyon and A.G. Pritchard (later Turnbull) but the majority seem to have been compiled by the 'Ionospheric Young Ladies'. There is an occasional note in Appleton's own hand. Some of the material remains in its original folders or wrappers, but most was received as loose sheets. It constitutes the background information for the various projects in Section Coll-37/C, but because of its large size and because it is not specifically referred to in the correspondence or drafts, it has been listed separately. The contents cover a wide range of subjects. The index covers only broad descriptive titles; any original groupings or headings have been preserved and are indicated by the use of inverted commas, but it has not been possible to furnish detailed descriptions, especially for loose sheets or fragmentary notes.