Hans Jenny (1904-1972) was a Basel-born physician who taught science at the Rudolf Steiner school in Zürich for four years before going into medical practice. He built the tonoscope and drove plates and membranes with crystal oscillators, and in one much-repeated experiment spread quartz sand on a 60-centimetre black drum membrane and sang loudly into it through a cardboard pipe.
His two volumes, Cymatics: The Study of Wave Phenomena, appeared in 1967 and 1972, the second in the year he died. They document sound acting on fluids, powders and pastes, and are the source of most of the images the field still circulates.
The article notes the influences — Alvin Lucier, György Kepes at MIT — and also categorises Jenny as an anthroposophist. That matters for reading him: his conclusion that vibration produces "a dynamic but ordered pattern" is descriptive, but his framing leans towards the metaphysical rather than the measurable.