The neutralization of acids by bases affords many illustrations, known even before the atomic theory, of the truth of the statement.
In 1828 James Wilson (author of the article Ornithology in the 7th and Wilson 8th editions of the present work) began, under the title of Illustrations of Zoology, the publication of a series of his own drawings (which he did not, however, himself engrave) with corresponding letterpress.
The plates of De Rossi, Perret, and, indeed, all illustrations of the catacombs, exhibit frequent examples of the same destructive superstition.
He gave amusing illustrations of the absurdity and poverty of the current pulpit oratory of his day, some of them being taken from the sermons of his own father.
Humboldt's concrete illustrations and the remarkable power of his personality enabled him to enforce these principles in a way that produced an immediate and lasting effect.