Galileo's Discorsi
and the fictive treatise De motu locali

Galileo's manuscript Ms. Gal. 72 predominantly contains notes, calculations, drawings, and drafts of different degrees of elaboration related to theorems and problems eventually published in his final work on mechanics, the Discorsi of 1638.

The Discorsi are written as a dialogue between Salviati, Sagredo, and Simplicio, continued over a number of Days which correspond to chapters of a fictive book. Galileo's spokesman Salviati quotes from a treatise on motion which is presented as a deductive theory and is written in Latin, while the discussions are conducted in Italian. This treatise, entitled De motu locali, is comprised of three books, the first two of which are contained in the Third Day of the Discorsi, while the Third Book is read in the Fourth Day. The First Book deals with the basic rules of kinematics, the second with the motion of fall and motion along inclined planes, and the third with projectile motion.

In view of the significance of the deductive structure of De motu locali for understanding the folio pages in Ms. Gal. 72, the electronic representation offers two features which make it possible to use this deductive structure for navigating through the manuscript.

First, the electronic representation includes a list of the propositions of De motu locali with links to:

Second, the electronic representation of the propositions of De motu locali is equipped with links mapping its deductive structure. In particular, the proof of each theorem contains links to other propositions which enter the proof as conditions.

In addition to the propositions explicitely stated as such in De motu locali we have included a list of other propositions which enter Galileo's arguments and proofs. These propositions are essentially treated in the same manner as the propositions of De motu locali with the exception that they are only mentioned as conditions in the reconstruction of the deductive structure of De motu locali with a short code, but without carrying a link.