Galileo, Dialogo sopra i Due Massimi Sistemi del Mondo (Florence, 1632)
This is Galileo’s witty and entertaining dialogue in defense of Copernicus. In the frontispiece, Aristotle and Ptolemy hold an Earth-centered armillary sphere (left). Copernicus holds a Sun-centered model of the universe (right). Just two systems appear in the Dialogo; Galileo nowhere mentions the Tychonic system then favored by most astronomers.
Galileo inserted statements about the hypothetical character of the work in the preface and conclusion. Nevertheless, the book as a whole was anything but even-handed, contrary to instructions issued to Galileo in 1616. Once published, Urban VIII gave orders for the Dialogo to be recalled and summoned Galileo to Rome for trial.
This copy is one of four first editions of Galileo held by OU which contain Galileo’s own handwriting.
– Salviati, named for a close friend of Galileo’s, defends the Copernican system with scientific brilliance and legendary wit. Master of both quantitative argument and experimental evidence, Salviati always seems ten steps ahead of anyone else. Never at a loss for words, Salviati clearly directs the flow of conversation.
– Sagredo, named after another friend of Galileo’s, represents an open-minded reader. As an inquisitive and bright student, he is not intimidated by Salviati, but comes up with insightful questions. Sagredo is the man in the middle; he desires neither to discard traditional authorities nor to embrace novelties unless there is compelling evidence.
– Simplicio, named after an ancient Greek commentator on Aristotle, ineptly defends the Earth-centered system. Simplicio frequently admits that he doesn’t understand an argument, and his requests for additional explanations provide comic relief along the way.
Galileo placed greatest emphasis in this book upon an argument for Copernicanism from the ebb and flow of the tides. This argument was physical in nature, based on causal explanation, rather than mathematical. It was an attempt to achieve a level of certainty which had proven elusive for mathematical methods alone. Unfortunately, the argument was not persuasive, then or now.
Most astronomers at the time were neither Ptolemaic nor Copernican, so Galileo displayed some chutzpah in rigging the debate as an exclusive choice between only two of the contemporary systems (see Cosmological Systems, Part 1).
One page displays a new sentence by Simplicio, handwritten in the margin, to go before a long paragraph by Salviati. This sentence is included in the second edition. Here it is written in Galileo’s own hand.
