The distribution of electrons in the undisturbed F2 later of the ionosphere

h'(f) curves recorded at Watheroo, Huancayo and Slough near midwinter, midsummer and equinox in years of sunspot maximum and minimum were analyzed so as to provide N(h) curves'which show the electron density (N) as a function of the height ( . The method of analysis is described and its limitations are discussed. The earth’s magnetic field has been neglected in the calculations; although this may lead to an error in some of the actual heights quoted, it should not cause appreciable error in the variation of those heights. Curves for the ‘international magnetically quietest days’ in each of the months analyzed are considered, and it is shown how, by a process of averaging, it is possible to deduce the form of a ‘mean quiet Flayer’. This represents the basic behaviour of the region on magnetically quiet days without those details which are peculiar to any one day. The resulting ‘ mean quiet F layers ’ are described in a series of curves. The detailed results, in tabulated form, are available from the Cavendish Laboratory for bona fide research workers.