Scientist of the Day - Mario Guiducci
Title page, Discorso delle comete, by Mario Guiducci (i.e., Galileo Galilei), with printer’s mark of Pietro Cecconcelli, 1619 (Linda Hall Library)
Mario Guiducci, an Italian scholar and a member of Galileo’s circle, was born in Florence on Mar. 18, 1583. He attended the Collegio Romano, the Jesuit university in Rome, and he appears to have studied at Pisa as well. Somewhere along the line, he met Galileo Galilei, and his student Benedetto Castelli, and Guiducci probably studied with one or both of them in the period following 1610, after Galileo published his Sidereus nuncius.
In 1618, between June and November, three comets appeared in the skies of Italy (and in the skies everywhere else, but we tell an Italian story today). A young Roman Jesuit astronomer named Orazio Grassi gave a lecture on all three comets at the Roman College, and then he published his talk in 1619 as De tribus cometis. He wrote anonymously, identifying himself only as one of the fathers of the Society of Jesus. In general, he built on the ideas of Tycho Brahe, who thought (unlike Aristotelians) that comets lie beyond the Moon and orbit the Sun. We told much of the story, in more detail, in a post on Grassi just last year, after we acquired a copy of De tribus cometis.
Binding, Discorso delle comete, by Mario Guiducci (i.e., Galileo Galilei), 1619, with armorial device of a later owne, Uberto Visconti di Modrone (Linda Hall Library)
Galileo had been sick for much of 1618, but he had recovered by the time Grassi’s book appeared, and he did not take it well. He had already had a run-in with one Jesuit astronomer, Christoph Scheiner, who also wrote under a pseudonym, and he was in no mood to listen to another, especially since he thought Brahe’s ideas on comets were nonsense. So Galileo wrote an intemperate reply to Grassi. Not wanting to do so under his own name, and, preferring not to use a pseudonym, he passed authorship to Guiducci and published his diatribe under Guiducci’s name as Discorso delle comete (1619). We acquired this book in 2023, from New Yok City bookseller Jonahan Hill (first image).
The theory of comets put forward by Guiduccj/Galileo in the Discorso was an odd one, in that they tried to argue that comets are not physical objects like planets, but rather optical phenomena, the result of exhalations from the Earth, which would explain why they exhibit no parallax. It was inherently less plausible than the suggestions of Tycho Brahe and the Jesuits, including Grassi. The title page is also notable for including the device of the printer, Pietro Cecconcelli, which consisted of the six-orb device of the Medici family, who would protect Galileo as best they could in the upcoming confrontation with the Church. The inclusion of the Medicean stars (the four new moons of Jupiter, discovered by Galileo) at the center is a nice touch.
These two books, the De tribus cometis and the Discorso, marked the onset of the so-called "controversy on comets," which culminated in the publication of Galileo's first treatise on scientific method, Il Saggiatore (The Assayer), which was Galileo's slow response (1623) to Grassi's more immediate reply, Libra astronomica (1619), written under the pseudonym Lothario Sarsi, about which we wrote a post in 2020, before we owned the first two books. If you look at the title page there, of the Libra, where Galileo is mentioned in the subtitle in large type, you will see that no one was fooled by the attributed authorship to Guiducci.
Chiesa di Ognissanti, Florence, where Mario Guiducci was buried (Wikimedia commons)
After Maffeo Barberini became Pope Urban VIII in 1623, Guiducci moved to Rome for several years, seeking preferment, unsuccessfully, but serving as an informant for Galileo as to what was going on in Rome, and he returned to Florence in 1625. He remained close to Galileo for the rest of both their lives, helping Galileo write his Dialogo (1632) and standing by him during the resulting trial (1633). Galileo died in 1642. Guiducci passed away on Nov. 5, 1646, leaving no portrait behind, and was buried in the chiesa di Ognissanti in Florence (third image), alongside Sandro Botticelli and Amerigo Vespucci, and under the watchful eye of the marvelous Saint Jerome, painted by Domenico Ghirlandaio in 1480 (last image).
St. Jerome in his Study, by Domenico Ghirlandaio, fresco, 1480, chiesa di Ognissanti, Florence, Web Galley of Art (wga.hu)
William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to ashworthw@umkc.edu.
