Reflections in Appleton´s mirror: a century of ionospheric science

From its beginnings in the nineteenth and early twentieth centuries, ionospheric physics evolved into a major branch of the wider discipline solar-terrestrial physics. This paper traces progress from the earliest days, through Appleton´s era and the International Geophysical Year up to the present. Several lines of research are foreseen along which ionospheric physics will advance into the next century