The optical Galilean interpretation of the antique Theophrastian model for plant diseases
Résumé
Galileo suggests in his 12 th Problema a new approach to explain the damages caused to plants exposed to weather. He applied the guidelines he had defined to the study of local motion change: namely, the establishment of a geometrical model representing the facts observed. Since Antiquity, the damage observed on vegetation had been essentially understood in terms of Theophrastus’ explanation of erusibe, and, but to a lesser extent, of Pliny the Elder’s rubigo, both according to the theory of decomposition from Aristotle. Galileo opts for the burning sphere model studied throughout the history of optics. Galileo’s text written about 1638, but only published in 1718, is the first of a series of texts, all through the 18 th century, approaching the explanation of diseases inspired from optics; texts which are inspired by Galileo’s 12 th Problem or which suggest another similar one, such as Stephen Hales’ and Pierre-Daniel Huet’s works, or which oppose it but with optic arguments, such as Michel Adanson’s or Felice Fontana’s
works. When Galileo conceives his models, his natural philosophy has come to maturity and the Aristotelian approach is strongly challenged in relation to the study of local motion. But the other changes, in particular those concerning living things, remain broadly studied according to Aristotelian principles. When Galileo 12 th Problema is posthumously published, aristotelianism is declining both for chemistry and the study of living things. This is after the emergence of Cartesian mechanism and the use of chemistry is developing for studying living things. The optics approach for the plant disease model ends by being marginalized, being too simple to explain the complex relationships between plants and climatic circumstances.
Then, this study helps us understand how unification between sky and earth, worked by the New Philosophy, failed to unify living and non-living things.