... In the 1800s it was already evident that the Earth's magnetic field was involved: auroral rays seemed to follow the Earth's magnetic field lines, and the frequency with which aurora was observed depended on the distance from the magnetic pole, not from the geographic one. ... That is the beginning of the ionosphere , a layer with enough free electrons (and ions) to play an important role in radio communications. ... The simplest atom is the one of hydrogen, with just one electron. ...