Newly discovered 1666 manuscript may trace four-lens telescope experiments to Galileo

A potentially history-altering finding by a University of Limerick researcher may provide the most detailed technical analysis of a telescope demonstrably made by the famous astronomer and scientist Galileo Galilei.

A previously unknown 17th-century description of a four-lens terrestrial telescope attributed to Galileo was discovered by Dr. José María Moreno Madrid, a researcher at UL’s School of History and Geography.

Dr. Moreno Madrid made the discovery while studying a 1666 manuscript written by a Spanish Dominican friar named Ignacio Muñoz. In a document titled De Tellescopiis Stellarum, Muñoz provided a component-by-component description of a four-lens telescope described as “fabricatum a Galilaeo,” or “manufactured by Galileo.”

Existing historical records place the first four-lens telescopes around 1643–45, with surveys of telescope production in Europe during the second half of the century suggesting that production became widespread from the 1640s onward.

Now, research published in the Annals of Science provides evidence suggesting that experimentation with the four-lens telescope took place earlier than previously believed or documented and could be attributed to Galileo himself.

A manuscript tied to New Spain

“If, as the text claims, the telescope analyzed was indeed manufactured by Galileo, then the earliest known experimentation with four-lens telescopes would have to be moved back to 1630 at the latest and credited to him. Moreover, Muñoz’s De Tellescopiis Stellarum would become the most detailed technical analysis of a telescope demonstrably made by Galileo—and, somewhat paradoxically, it would concern a four-lens telescope rather than the Galilean design that ultimately came to bear his name,” Moreno said.

According to Muñoz’s manuscript, the telescope was presented to him by Antonio Sebastián de Toledo Molina y Salazar, then viceroy of New Spain and Marquis of Mancera, as part of a test of Muñoz’s scientific capabilities.

Having been exiled in Portuguese India for his role in an attempt to illicitly establish a new order of Dominican friars in the Philippines, where he had first traveled from Spain, Muñoz had written to the Spanish king, Philip IV, promising a revolutionary nautical proposal to improve the performance of the Hispanic fleets around the globe. In exchange, the monarch would sponsor his return to his homeland via the Manila Galleon, with its customary stopover in New Spain.

The viceroy of New Spain, suspicious of Muñoz’s scientific skills and concerned that he might be tricking the king into funding his travels, ordered him to meticulously analyze the instrument. Muñoz provided a detailed description of a reverse-tapered four-lens terrestrial telescope with an erecting eyepiece and convex lenses separated by twice their focal lengths. Crucially, the manuscript entry also includes detailed diagrams and drawings of the instrument.

Gaps in Galileo’s telescope record

Galileo famously insisted that he had never and would never sell any of his telescopes. None of the eight telescopes manufactured in the first half of the 17th century that have survived to the present day can unequivocally be attributed to him. Two telescopes housed in the Museum of Florence have been credited to him, but the attribution is not universally accepted. Galileo also did not leave behind any technical analyses of his own telescopes.

According to historical accounts, Galileo presented one large and two smaller telescopes to Philip IV and his wife in a bid to curry favor at court and improve his chances of claiming the generous reward offered for solving the so-called “problem of longitude.” Moreno suggests that the four-lens telescope outlined in Muñoz’s manuscript, if indeed crafted by Galileo, may have come into the possession of the Marquis of Mancera as a gift from the Spanish royal family in recognition of his diplomatic and political successes for the court in Madrid.

With no further mention of the telescope in Mancera’s correspondence with the Spanish court, this document presents evidence that could shift our understanding of the history of early modern telescopes, and Galileo’s in particular.

Moreno said, “I believe that the unambiguous attribution of the telescope in the manuscript, together with the documentary evidence that three telescopes made by Galileo—whose optical configurations remain unspecified—may have been accessible to Mancera through his connections at the Spanish court, at the very least invites consideration of this possibility.”

Evidence that broadens the archive

Moreno also emphasized the importance of Muñoz’s status and capabilities as a scholar with a background in math and astronomy, adding that there is no reference to an optical configuration such as this in any existing documentation produced or associated with either Galileo or any of his contemporaries.

Whether or not the telescope can be definitively attributed to Galileo, Moreno says Muñoz’s manuscript is significant in expanding the knowledge base for technical descriptions of 17th-century telescopes and underscoring these instruments as objects of prestige at the time.

Now, Moreno hopes his research will form the basis of further exploration and discovery: “It is to be hoped that new documentary or material evidence will soon emerge to confirm the telescope’s attribution and further enhance our understanding of it.”

Who’s behind this story?

Gaby Clark

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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