A 1666 Manuscript Describes a Four-Lens Telescope 'Manufactured by Galileo'

No telescope surviving anywhere in the world can be attributed to Galileo Galilei beyond dispute, and Galileo himself left no technical analysis of the instruments he built. A manuscript written in 1666 by a Spanish friar may be the closest thing anyone has found to one.

Jose Maria Moreno Madrid, a researcher in the School of History and Geography at the University of Limerick, identified the document while working on the papers of Ignacio Munoz, a Dominican who spent years in the Spanish colonies pressing the crown to fund his work on navigation. The text, titled De Tellescopiis Stellarum, contains a component-by-component description of a four-lens terrestrial telescope, with diagrams, and labels it fabricatum a Galilaeo — manufactured by Galileo. The research is published in Annals of Science.

Munoz's account of how the instrument came into his hands is specific. He writes that the viceroy of New Spain handed him the telescope as a test of his competence, at a moment when Munoz was seeking royal sponsorship for his nautical innovations and had every reason to demonstrate that he could take an optical instrument apart and explain it.

The date is what makes the document interesting rather than merely charming. A four-lens terrestrial telescope inverts the image twice, so the view comes out right side up — essential for use on land or at sea, and a meaningful step past the two-lens Galilean design that shows a small, upright field, or the Keplerian design that shows a wider but inverted one. The earliest four-lens telescopes in the historical record date to roughly 1643 to 1645, years after Galileo's death in 1642. If Munoz's instrument was what he says it was, Galileo was experimenting with the configuration by 1630 at the latest.

"The most detailed technical analysis of a telescope demonstrably made by Galileo" is how Moreno characterizes the manuscript's potential significance — with the emphasis on potential. He is explicit about the caveats. The attribution rests on a claim made 24 years after Galileo died, by a man with a motive to impress his patrons, about an object that no longer exists.

What supports it is that Galileo is documented to have presented telescopes to Spanish royalty. He spent years lobbying the Spanish crown to adopt his method of determining longitude at sea using the moons of Jupiter, and instruments were part of that campaign. A Galilean telescope reaching a viceroy in Mexico City by the 1660s is not a stretch.

Moreno says corroborating evidence will have to come from elsewhere in the Spanish archives — inventories, correspondence, customs records — and that the search is now the obvious next step. Historians of science have spent four centuries reconstructing Galileo's optics largely from his letters and from two surviving instruments in Florence whose provenance is itself argued over. A detailed technical drawing, made by someone who had the object in front of him, would be a different class of evidence.