Signedunsigned
Inscribedon hinge: coat-of-arms of the Gonzaga family
FunctionThis instrument was designed to make a wide variety of geometrical and arithmetical calculations. It used the properties of similar triangles (trigonometry) as the basic mathematical principle.
A video with information on the use of Galileo’s compass, produced by Museo Galileo, is available on their website here.
Historical AttributesThis is one of the few surviving examples of Galileo's geometrical and military compass, a form of sector invented by Galileo in 1597. The instrument was likely made by Galileo's personal instrument maker, Marc'Antonio Mazzoleni, who was installed at Galileo's house since 1598.
During the winter of 1603-1604, Galileo visited the court of the Vincenzo Gonzaga, the Duke of Mantua, in an effort to obtain a position there. He impressed the Duke with a gift of this geometrical and military compass, which is inscribed with the Duke's coat of arms on the hinge, and an instruction manual for the instrument. The Duke offered Galileo a salary of 300 ducats per year plus living expenses for himself and a servant. At this time, Galileo's salary at the University of Padua was 320 ducats, and he had further income from his boarding students, to whom he sold his geometrical compass and trained in the use of it. Galileo therefore requested instead a salary of 500 ducats with an expense account for himself and two servants. No terms could be worked out, and Galileo stayed at his post in Padua.
The Duke of Mantua did give Galileo a gold chain with a medal, plus two silver dishes. It was the custom that the medal could not be sold but that the chain and the cups could. In his account books for 1604, Galileo put down the chain for 900 lire and the cups for 440 lire.
Primary SourcesGalileo Galilei, Le operazioni del compasso geometrico et militare (Padua, 1606).
ProvenancePurchase by David P. Wheatland, Topsfield, 1952; gift to CHSI, 1984.
Published ReferencesEva Koleva Timothy, Lost in Learning: The Art of Discovery (Newburyport, MA: Athenaeum Publishing, 2010).