Threshold to space - Early studies of the ionosphere

Early concepts of the form or profile of electron density above the earth in the ionosphere and the effects of radio measuring instruments upon those concepts are examined. Trans-Atlantic radio communications resulted in various descriptions of an upper conducting atmospheric layer and ionospheric radio soundings led to the discovery of various layers, each reflecting back pulses up to a certain critical frequency. Models developed to fit these layers, especially Chapman's along with the important contributions of Appleton, are discussed. Efforts to construct ionization profiles are assessed and future research prospects are discussed