ABSTRACT
By the turn of the twentieth century it had become clear that beyond-the-horizon transmission and reception of wireless signals were being made possible by some unknown factor. The transatlantic experiments of 1901 turned the attention of various researchers, notably Heaviside, Kennelly and Marconi, towards the problem of providing a theory to account for the phenomenon. The ionosphere explanation offered by the two former and endorsed by the latter proved, in the event, to be an accurate assessment, but it was not until the 1920s by the efforts of Edward Appleton, Barnett, Breit, Tuve, T. L. Eckersley and others, that the physical existence of the reflecting layers was proven beyond dispute.
