In 1563, della Porta published
De Furtivis Literarum Notis, a work about
cryptography. In it, he described the first known digraphic
substitution cipher.
Charles J. Mendelsohn commented: Della Porta invented a method which allowed him to write secret messages on the inside of eggs. Some of his friends were imprisoned by the Inquisition. At the gate of the prison, everything was checked except for eggs. Della Porta wrote messages on the eggshell using a mixture made of plant pigments and
alum. The ink penetrated the eggshell which is semi-porous. When the eggshell was dry, he boiled the egg in hot water and the ink on the outside of the egg was washed away. When the recipient in prison peeled off the shell, the message was revealed once again on the egg white.
De Furtivis Literarum Notis also contains one of the earliest known examples of
music substitution ciphers. In 1586 della Porta published a work on
physiognomy,
De humana physiognomonia libri IIII (1586). This influenced the Swiss eighteenth-century pastor
Johann Kaspar Lavater as well as the 19th-century criminologist
Cesare Lombroso. Della Porta wrote extensively on a wide spectrum of subjects throughout his life – for instance, an agricultural encyclopedia entitled "Villa" as well as works on
meteorology,
optics, and
astronomy. In 1589, on the eve of the early modern Scientific Revolution, della Porta became the first person to attack in print, on
experimental grounds, the ancient assertion that
garlic could disempower magnets. This was an early example of the authority of early authors being replaced by experiment as the backing for a scientific assertion. Della Porta's conclusion was confirmed experimentally by
Thomas Browne, among others. In later life, della Porta collected rare specimens and grew exotic plants. His work
Phytognomonica lists plants according to their geographical location. In
Phytognomonica the first observation of fungal spores is recorded, making him a pioneer of
mycology. His private museum was visited by travellers and was one of the earliest examples of
natural history museums. It inspired the
Jesuit Athanasius Kircher to begin a similar, even more renowned, collection in Rome. ==Pioneering scientific society==