Balser & Wagner (1960) — first experimental confirmation

In 1960 Martin Balser and Charles A. Wagner carried out the first spectral measurement of the natural electromagnetic background in the ELF band and experimentally confirmed the existence of the resonances of the Earth-ionosphere cavity that Schumann had predicted theoretically (#9). Balser 1960

Their measurement demonstrated a characteristic series of resonance peaks in the spectrum — that is, that the natural electromagnetic field really does exhibit pronounced maxima at the expected frequencies. This turned Schumann's prediction from a theoretical hypothesis into an observed, verifiable phenomenon. The work of Balser and Wagner is therefore considered the founding experimental milestone of the entire field and is the starting point for all later research (#13).