Reading Galileo's Dialogue Comparing the Ptolemaic and Copernican Systems

This is the book that got Galileo into trouble

In the popular consciousness, upon hearing about Galileo, one thinks about the confrontation that he had with the Holy Inquisition of the Roman Church, and his subsequent condemnation in 1633 to house arrest, under which he lived until his death in 1642. The book that led to this confrontation was his Dialogue concerning the two chief world systems — Ptolemaic and Copernican¹ (Dialogo sopra i due massimi sistemi del mondo Tolemaico, e Coperniciano).

I am currently reading the Dialogue. The book is organized as three friends, Salviati, Sagredo and Simplicio, meeting over four days to discuss the relative merits of the Aristotelian/Ptolemaic and Copernican systems. Each day corresponds to a chapter in the book, and a wide variety of topics is covered.

The three characters are as follows:

• Salviati is named after Galileo’s friend Filippo Salviati (1582–1614). The personage represents Galileo, often referring directly to him as the "Academician" in honor of his membership in the Accademia dei Lincei.

• Sagredo is named after Giovanni Francesco Sagredo (1571–1620). The personage represents an interested bystander who wants to learn more.

• Simplicio is named after Simplicius of Cilicia, a sixth-century commentator on Aristotle. The name also can easily be understood as “simpleton” or “simple-minded”. The personage systematically puts forward the Aristotelian/Ptolemaic position.

I intend to write a post for each of the four days, focusing on both technical and epistemological issues that arise therein. The content is fascinating, as is the style of writing.

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1. Galileo Galilei. Dialogue concerning the two chief world systems — Ptolemaic and Copernican. Translated by Stillman Drake, foreword by Albert Einstein. University of California Press, 2nd ed., 1967.