Mario Otto Helbing, Pier Daniele Napolitani

Young Galileo Between Ptolemy and Copernicus

It is well known that in 1597 Galileo was “by long time'' Copernican (“In Copernici sententiam multis ab hic annis venerim”, Galileo to Kepler, August 4, 1597). The purpose of this paper is to investigate if it is possible to be more precise in dating his conversion to Copernicanism. In our opinion this it is not a chronological curiosity, because it seems somewhat relevant to understand in which philosophical and scientific context and in which framework of studies and research Galileo espoused the heliocentric theories. The Copernicanism was one of the foremost tracts of the whole Galilean thought and clarify that context and that framework could cast some light on the intricate puzzle about Galileo's early scientific career.

We shall prove (mainly on the basis of a letter of Galileo to Jacopo Mazzoni, May 1597) that the conversion to Copernicanism took place at the end of the so-called “Pisan period'' and after the latest writings contained in Galileo's De motu antiquiora. This result allows us to elaborate the following conclusions:

— the De motu antiquiora are, beyond any reasonable doubt, to be ascribed to the “Pisan period'';
— Galileo's early Copernicanism has to be connected with the philosophical discussions about the movement which were very lively in late 16th-century Pisa;
— Galileo's giving up of the publication of his De motu was possibly caused by his conversion to heliocentric theories.

Mario Otto Helbing received his Ph.D. at the Scuola Normale Superiore of Pisa. He is the author of La filosofia di Francesco Buonamici, professore di Galileo a Pisa, Pisa 1989; All’alba della scienza galileiana: Michel Varro e il suo “De motu tractatus”, Cagliari 2000 (with M. Camerota). He co-edited (with O. Besomi) the new critical and commentated editions of G. Galilei, Dialogo sopra i due massimi sistemi del mondo, Padua 1998, and G. Galilei and M. Guiducci, Discorso delle comete, Padua 2002.

Pier Daniele Napolitani has been a professor of the History of Mathematics at the University of Pisa since 1992. His research has focused on the 16th and 17th centuries, in particular on the birth of modern mathematical sciences and the renunciation of the natural philosophy of Antiquity and the Middle Ages. He co-edited (with U. Baldini) the critical edition of Christoph Clavius’ correspondence, Pisa 1992, and published many works on Luca Valerio and Galileo Galilei. He organized the Ateliers De Motu Antiquiora (Pisa-Nice, 1994-98) together with P. Souffrin and many workshops on the diffusion of Viate’s algebra in Italy. At present, he is the director of the critical edition of mathematical works by Francesco Maurolico.