An antique brass plumb level with engraved markings, a curved scale, and a hanging plumb bob against a black background.

| Photograph © Collection of Historical Scientific Instruments, Harvard University

Scientific Stardom

How Galileo used a simple tool to shape his fame and fortune

Before Galileo Galilei turned his telescope skyward, he had already begun to burnish his reputation on the ground with another invention: a geometric and military compass. He began work on the device—known today as a sector, with two legs and a plumbline—in the 1590s. The concept already existed, but Galileo vastly improved the basic design by adding extra scales for greater precision and versatility. His version could be used by artillerymen to determine the cannon angles needed to hit certain targets; it could also be deployed quickly to calculate other proportional measurements, like cube roots and compound interest.

a
Detail of the compass | Photograph © Collection of Historical Scientific Instruments, Harvard University

His compass became “a tool of power,” says professor of the history of science Hannah Marcus: it turned Galileo into “one of the first celebrity scientists.” He sold roughly 100 of them; he also wrote and published a manual of sorts in 1606. But he left out key details, Marcus says: “You can’t really figure it all out from the manual.” So those who wanted to learn how to use the compass paid for private lessons—a side job that earned Galileo three times his salary as a mathematics professor at the University of Padua. Marcus summarizes: “He’s getting rich off of this thing.”

a
Detail of the compass  |  Photograph © Collection of Historical Scientific Instruments, Harvard University

The device also served to advance Galileo’s ambition. The compass shown—on display at Harvard’s Collection of Historical and Scientific Instruments, which Marcus directs—features the coat of arms of the Gonzaga family. In 1604, Galileo gifted this compass to Federico II Gonzaga, Duke of Mantua, likely in an attempt to curry favor and secure a court position. This act foreshadowed a similar one in 1610, when he presented his newly invented telescope to the Medici family—ultimately earning him the title of court philosopher and mathematician. “The big innovation here,” Marcus says, “is the way that he’s using this instrument, his own personal expertise, and [the medium of] print to manage his own fame and access to scientific knowledge.”

The story of the compass illuminates a lesser-known chapter of Galileo’s life—and serves as a reminder that even history’s greatest minds understood the art of branding. Long before his name became synonymous with the heavens, Galileo was busy calculating his own ascent, one proportion at a time. 

Click here for the March-April 2025 issue table of contents

Read more articles by Nina Pasquini

You might also like

Harvard Releases Antisemitism and Anti-Muslim Task Force Reports

University publishes findings from thorough examinations of campus conditions.

Harvard Renames Diversity Office

The decision follows pressure from the Trump administration to eliminate DEI practices. 

Centralizing University Discipline

Harvard establishes new disciplinary procedures for campus protest violations.

Most popular

Harvard Renames Diversity Office

The decision follows pressure from the Trump administration to eliminate DEI practices. 

Harvard Releases Antisemitism and Anti-Muslim Task Force Reports

University publishes findings from thorough examinations of campus conditions.

The New Gender Gaps

What to do as men and boys fall behind

Explore More From Current Issue

The Trump Administration's Impact on Higher Education

Unprecedented federal actions against research funding, diversity, speech, and more

89664

Jessica Shand—Math and Music at Harvard

Jessica Shand blends math and music.

89677

Paper Peepshows at Harvard's Baker Library

How “paper peepshows” brought distant realms to life

89684