Tonal studies of bells ancient and modern

In 1978 Hervey Bagot constructed his own portable electronic equipment for the study of the "partial tones" in bells. Shown are his results for a South Australian tower (St Andrew's, Walkerville) and a British tower (Wellington St Margaret's, Herefs.). Some of the older bells display doublets, i.e. the presence of two frequencies in the same mode of vibration. Doublets show up as "beating" in a bell's sound.
The thin vertical lines in the graphics indicate the "ideal" "octave-hum/minor-third" tonal structure. H = hum note; S = strike note; P = prime; T = tierce; Q = quint; N = "nominal' (also known as "octave").