The Works of Galileo

A New Pope and a New Dialogue

The Assayer, 1623

In 1616 Galileo may have been silenced on Copernicanism, but he bounced back with gusto in 1623. In that year his supporter and friend, Cardinal Maffeo Barberini, a former patron of the Lynx and uncle of Cardinal Francesco Barbarini, became Pope Urban VIII. The election of Barberini seemed to assure Galileo of support at the highest level in the Church. A visit to Rome confirmed this.

The title page of The Assayer, (Figure 1) shows the crest of the Barbarini family, featuring three busy bees. In The Assayer, Galileo weighs the astronomical views of a Jesuit, Orazio Grassi, and finds them wanting. The book was dedicated to the new pope. The title page also shows that Urban VIII employed a member of the Lynx, Cesarini, at a high level in the papal service. This book was edited and published by members of the Lynx.

Again Galileo insisted that physics should be mathematical. According to the title page, he was the philosopher or physicist of the Grand Duke of Tuscany, not merely the mathematician. Physics or natural philosophy spans the gamut from processes of generation and growth (represented by the plant) to the physical structure of the universe, represented by the cosmic cross-section. Mathematics, on the other hand, is symbolized by telescopes, and an astrolabe. This is the book containing Galileo’s famous statement that mathematics is the language of nature. Only through mathematics can one achieve lasting truth in physics. Those who neglect mathematics wander endlessly in a dark labyrinth.

“Philosophy [i.e., physics] is written in this grand book--I mean the universe--which stands continually open to our gaze, but it cannot be understood unless one first learns to comprehend the language and interpret the characters in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometrical figures, without which it is humanly impossible to understand a single word of it; without these, one is wandering around in a dark labyrinth.” Galileo Galilei, Il Saggiatore (The Asssayer, 1616)

Although The Assayer contains a magnificent polemic for mathematical physics, ironically its main point was to ridicule a mathematical astronomer. This time, the target of Galileo’s wit and sarcasm was the cometary theory of a Jesuit, Orazio Grassi, who argued from parallax that comets move above the Moon. Galileo mistakenly countered that comets are an optical illusion.

(Figure 2) (Figure 3) (Figure 4) (Figure 5) (Figure 6)

Galileo’s polemical tone sealed the opposition of the Jesuit order to Galileo. However, the book was read with delight at the dinner table by Urban VIII, who had written a poem lauding Galileo for his rhetorical performances.

(Figure 7) is Galileo’s first published drawing of the phases of Venus.

English trans. Stillman Drake and C. D. O’Malley, in The Controversy on the Comets of 1618 (University of Pennsylvania Press, 1960).

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Galileo, The Assayer, 1623. Title page.

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Galileo, The Assayer, 1623. Frontispiece.

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Galileo, The Assayer, 1623. First page.

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Galileo, The Assayer, 1623. Page 114.

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Galileo, The Assayer, 1623. Page 118.

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Galileo, The Assayer, 1623. Page 130.

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Galileo, The Assayer, 1623. Page 217.

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Exhibit credit: Kerry Magruder, with the assistance of , Marilyn B. Ogilvie, Duane H. D. Roller.

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