Lost 1666 manuscript may hold the most detailed technical analysis of a telescope made by Galileo

A previously unknown seventeenth-century description of a four-lens terrestrial telescope attributed to Galileo Galilei has been unearthed by a researcher at the University of Limerick, and if the manuscript’s attribution holds, it could rewrite a familiar chapter in the history of the telescope. The discovery, made by Dr José María Moreno Madrid of UL’s School of History and Geography, is now published in the journal Annals of Science, and it centres on a document written in 1666 by a Spanish Dominican friar named Ignacio Muñoz.

The document, titled De Tellescopiis Stellarum, contains a component-by-component description of a four-lens telescope described in the manuscript as ‘fabricatum a Galilaeo’, or ‘manufactured by Galileo’. According to the research, this single entry would, if its attribution is accepted, constitute the most detailed technical analysis of a telescope provenly made by Galileo – and, somewhat paradoxically, it would concern a four-lens design rather than the two-lens Galilean configuration that ultimately came to bear his name.

The historical stakes are considerable. Existing records situate the first four-lens telescopes at around 1643 to 1645, and surveys of telescope production in Europe during the second half of the seventeenth century suggest that such instruments became widespread from the 1640s onwards. Dr Moreno Madrid’s research provides evidence suggesting that experimentation with the four-lens telescope took place earlier than previously believed and documented, and that it could be attributed to Galileo himself. ‘If, as the text claims, the telescope analysed was indeed manufactured by Galileo, then the earliest known experimentation with four-lens telescopes would have to be pushed back to 1630 at the latest and credited to him,’ Dr Moreno Madrid said.

The manuscript itself carries an extraordinary provenance story. According to Muñoz’s account, 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. Muñoz had travelled from Spain to the Philippines, where he played a role in an attempt to illicitly establish a new order of Dominican friars, and was subsequently exiled in Portuguese India. From there, he wrote 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 analyse the instrument. What Muñoz produced was a detailed description of a reverse-tapered four-lens terrestrial telescope with an erecting eyepiece, in which convex lenses were separated by twice their focal lengths. Crucially, the manuscript entry also includes detailed diagrams and drawings of the instrument, making it a rare and rich technical record of an early modern optical device.

The attribution to Galileo rests on more than the manuscript’s own claim. Galileo famously insisted that he had never, and would never, sell any of his telescopes. Of the eight telescopes manufactured in the first half of the seventeenth century that have survived to the present day, none can unequivocally be attributed to him; two telescopes residing in the Museum of Florence have been credited to him, but that attribution is not universally accepted. Moreover, Galileo did not leave behind any technical analyses of his own telescopes. A detailed, illustrated technical description of an instrument ‘manufactured by Galileo’, written by a contemporary scholar, would therefore fill a conspicuous gap in the documentary record.

How a Galileo telescope might have reached the viceroy of New Spain is a question the research also addresses. According to historical accounts, Galileo presented one large and two smaller telescopes to Philip IV and his wife in a bid to curry favour at court and improve his chances of claiming the generous reward offered for solving the so-called ‘problem of longitude’. Dr Moreno Madrid suggests that the four-lens telescope outlined in Muñoz’s manuscript, if indeed crafted by Galileo, may have come into the hands of the Marquis de Mancera as a gift from the Spanish royal family, in recognition of his diplomatic and political successes for the court in Madrid.

The evidence remains circumstantial, and Dr Moreno Madrid is careful about the strength of the claim. With no further mention of the telescope in the Marquis de Mancera’s correspondences with the Spanish court, this sole document presents evidence that could shift our understanding of the history of early modern telescopes, and of Galileo’s in particular. ‘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 configuration remain unspecified – may have been accessible to Mancera through his connections at the Spanish court, at the very least invites consideration of this possibility,’ Dr Moreno Madrid said.

Dr Moreno Madrid also emphasised the importance of Muñoz’s status and capabilities as a scholar with a background in mathematics and astronomy, lending weight to the technical content of the description. Notably, there is no reference to an optical configuration such as the one described in the manuscript in any existing documentation produced or associated with either Galileo or any of his contemporaries. That silence in the surviving record cuts both ways: it means the manuscript offers something genuinely new, but it also means the attribution cannot yet be corroborated from other sources.

Whether or not the telescope can be definitively attributed to Galileo, Dr Moreno Madrid argues that Muñoz’s manuscript holds significant importance in expanding the knowledge base for technical descriptions of seventeenth-century telescopes, and in underscoring these instruments as objects of prestige at the time. The research, published under the article title ‘De Tellescopiis Stellarum (1666). Was Galileo experimenting with four-lens terrestrial telescopes by 1630?’, is framed as an invitation to further inquiry rather than a settled conclusion. ‘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,’ Dr Moreno Madrid said.

Subject of Research: A historical study of a 1666 manuscript describing a four-lens terrestrial telescope attributed to Galileo

Article Title: University of Limerick, Ireland, researcher’s discovery may alter history with the ‘most detailed technical analysis’ yet of a Galileo telescope

Article References: University of Limerick, Ireland, researcher’s discovery may alter history with the ‘most detailed technical analysis’ yet of a Galileo telescope. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: Galileo Galilei, telescope, history of science, seventeenth century, Ignacio Muñoz, De Tellescopiis Stellarum, Annals of Science, optics, University of Limerick, manuscript, four-lens telescope, early modern science