First published in 4 books in 1558, and then in the expanded 20 book version of 1589, Porta's treatise partly represents work he undertook at the Accademia dei Segreti, which he founded, and is on subjects as diverse as "the Generation of Animals," and "Production of new Plants," "Increasing Household-Stuff," "the Wonders of the Lode-stone," "strange Cures," "Beautifying Women," "Fishing, Fowling, Hunting," "Invisible Writing," "Strange Glasses," "Pneumatick Experiments," and, finally, "Chaos." Although there was a strong portion of credulity mixed with Porta's empiricism, he was, as Norman states, "the first to add a concave lens to the aperture of the camera obscura, and his comparison of the camera lens to the pupil of the eye provided an easily understood demonstration that the source of visual images lay outside the eye, thus ending a centuries-old controversy."