This essay works through a genre of nineteenth-century popular science books aimed at children and amateurs, in which the newly settled physics of sound was sold as both instruction and entertainment. Chladni opens it: a metal plate, a violin bow, some sand, and shapes that looked arranged by invisible hands.
Thompson's argument is that the experiment mattered because it settled something. Sound was shown to be waves travelling through air and matter rather than particles emitted into it, and it was cheap enough that anyone with a copper plate could check. By 1901 Annie Besant and Charles Leadbeater could describe Chladni figures as already familiar to every student of acoustics — which is also a warning about how quickly the imagery was absorbed into theosophy.
Note one wrinkle: the essay dates Chladni's experiment to 1777, whereas his book appeared in 1787. Published October 2025.