Mirror in the sky

A story of research and discovery which, through the work of such scientists as Hertz, Marconi, Heaviside and - more particularly - Sir Edward Appleton, has led to the development of modern radio-communications. Some of the techniques which owe their origin to Appleton’s concept of the ionosphere are now being applied to radar, to reliable world-wide radio links, and more recently, to the science of radio-astronomy.