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Oratio Grassi, Tractatus de sphaera (Rome, 1623), ms.

Treatise on the Sphere

In the same year that Galileo published The Assayer, Grassi delivered these lectures to Jesuit students in the Rome College (Collegio Romano). Grassi describes Galileo’s discovery of mountains on the Moon, discusses the satellites of Jupiter, and interprets sunspots as imperfections on the surface of the Sun. This manuscript, never published and new to scholars, was acquired in 2012 through the generous support of the OU Athletic Department.

Grassi had argued publicly that comets are farther away than the Moon, which in itself was contrary to Aristotle, but what else might Grassi have been teaching young Jesuits behind closed doors? And how did he respond to Galileo’s public criticisms?  Documentary sources for astronomy at the Collegio Romano are notably scarce; this manuscript is one of only a few astronomical manuscripts from the leading Jesuit university preceding the publication and subsequent condemnation of Galileo’s Dialogo (1632).

Galileo's World Exhibition Location

Source: History of Science Collections

Section: Controversy

Section Number: 3

Object Number: 34

Subject Area(s): History of the Book, Astronomy, Physics, Mathematics, Manuscripts and Annotations

Time Period: 17th Century

Region(s): Europe, Italy

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