Original folder labelled in the hand of A.G. Turnbull (formerly Pritchard) 'I.G.Y. fF₂ Bartels Diagram'. The work relates to various projects based on an analysis of data assembled during the International Geophysical Year, and in particular to Appleton's paper presented at the U.R.S.I. meeting at Brussels, September 1959 on 'The Daily Variability of F₂ Layer Maximum Ionisation during the I. G. Y.' Appleton's chief collaborators in this work were A. G. Turnbull and C.P. Bell, and the 'Ionospheric Young Ladies' who prepared data and tables. Much of the material in 'General Ionospheric Topics' also refers to these projects, and there is additional data in Section Coll-37/F. Appleton also presented at the Brussels meeting a paper on 'Equatorial anomalies in the F₂ layer of the ionosphere', published in the Proceedings.