The Borghesi astronomical clock, as Silvio A. Bedini presents it, is not merely a timekeeping device but a mechanical embodiment of a cosmological system. Bedini’s study, drawn from the Smithsonian’s Museum of History and Technology, focuses on the clock’s construction and the intellectual context of its maker, Father Francesco Borghesi. The clock’s dials and moving parts are described with technical precision, revealing how Borghesi translated his geocentric model into brass and steel.

A Clock That Models the Heavens

Bedini emphasizes that the Borghesi clock was designed to represent a specific astronomical system, one that Borghesi himself devised. The clock’s primary function was not to tell hours but to display the motions of celestial bodies according to Borghesi’s theory. The author quotes Borghesi’s own description of his system, where he asks the reader to imagine “a kind of spherical convexity” and “two most sturdy poles” that hold the earth suspended by magnetic power. This passage, included in the excerpts, shows how the clock’s mechanism was intended to mirror a theoretical model. Bedini notes that the clock’s dials include indicators for the zodiac, the sun, and the moon, all arranged to reflect Borghesi’s vision of a universe centered on a stationary earth.

The Language of Craftsmanship

Bedini’s prose is marked by a careful attention to the materials and techniques of clockmaking. He describes the clock’s frame as being constructed of brass and iron, with gears and pinions cut to precise specifications. The author notes that the clock’s “greatest circles” are engraved with degrees and minutes, forming a “spherical net” for tracking celestial coordinates. This language echoes Borghesi’s own description of the Primum Mobile as a “great spherical net, extended to capture the longitude and latitude of the stars.” Bedini’s choice of words—such as “convexity,” “colure,” and “ecliptic”—mirrors the technical vocabulary of 17th-century astronomy, grounding the reader in the period’s scientific discourse.

Borghesi’s Magnetic Universe

A striking feature of Bedini’s account is his treatment of Borghesi’s magnetic cosmology. The clock’s mechanism, Bedini explains, was designed to demonstrate how the earth is held in place by two magnetic points, one boreal and one austral. These points, located in the zodiacal signs of Gemini and Sagittarius, exert equal pull on the earth’s axis, preventing it from moving closer to either. Bedini quotes Borghesi’s instruction to imagine the earth’s axis as iron and the magnetic points as having “some power (imagine it is magnetic power).” This speculative element, unusual for a clock, is presented by Bedini as a key insight into Borghesi’s creative process, blending mechanical ingenuity with natural philosophy.

Reading the Clock’s Dials

Bedini provides a detailed breakdown of the clock’s dials and their functions. The main dial, he notes, displays the hours and minutes, but also includes a rotating zodiac ring and an indicator for the sun’s position. A second dial shows the phases of the moon, while a third tracks the nodes of the moon’s orbit. The author points out that the clock’s “equinoctial colure” and “solstitial colure” are marked on the dials, allowing the user to read the positions of the equinoxes and solstices. Bedini’s description is methodical, walking the reader through each component without assuming prior knowledge of horology. He highlights the clock’s dual role as a scientific instrument and a decorative object, noting the engraved details on its face.

Bedini’s study offers a focused look at a single artifact, but it opens onto broader questions about the relationship between science and craft in the 17th century. Readers interested in the history of astronomy or early modern instrument-making will find here a concrete example of how theoretical ideas were given physical form. The excerpts provided are sufficient to appreciate Bedini’s methodical approach and his respect for Borghesi’s ingenuity, though the full text likely contains further details on the clock’s provenance and restoration.