365daysDate: May 19, 2009

Title: When Did Galileo Really Learn About the Telescope?


Podcaster: Mark Thompson

Organization: Galileo 1610

Description: Galileo hears about the invention of devices in the Netherlands for seeing faraway things as though nearby.

Bio: Mark Thompson, a professional cantor and amateur astronomer, has appeared as Galileo on radio, at community theatres and libraries, public schools, colleges and universities throughout the country. He has performed as Galileo for civic organizations, astronomy association conventions, marketing and outreach programs as well as private events and parties since 1996.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Anonymous on behalf of The Onion Router Project. The Onion Router Project provides free, open source software securing privacy on the Internet for all of Earth’s inhabitants. Find out more at


When did Galileo really learn about this strange device that made objects appear as if they were closer?

In Siderius Nuncius, Galileo’s history making pamphlet published in April 1610, Galileo claims he first heard a rumor about the Dutch perspicillum, or spyglass in May of 1609 and that this rumor was corroborated in a letter he received from a former student now living in Paris, one Jaques Badovere — but various historians have speculated that Galileo may have known about the Dutch spyglass much earlier than May of 1609, probably through his friend and confidant, Paolo Sarpi who seemed to have his finger on the pulse of European scientific and cultural developments.

As we mentioned in our previous podcast: as early as February, 1609—in an effort to gain more intimate access to the Tuscan court– Galileo wrote this letter to a friend well connected to the Medici family. Should we dismiss the following language as pure self-promotional hype?

“I have various inventions of which one alone should a great prince take delight in it, might suffice to place me above want for the rest of my life. Daily I discover new things, and if I had more leisure, and were able to employ more workmen, I should do much more in the way of experiment and invention.”

Is it possible that as the year began, Galileo was already working on some kind of vision-enhancing device of his own? Furthermore, might we assume from these remarks that either Galileo already had or was seeking a workman who might be more skilled than himself in optics and lens-making?

In his wonderful retrospective work: Stargazer:The Life and Times of the Telescope, Fred Watson states that although Galileo may not have been acquainted with the modern laws of refraction, he was a mathematician and was certainly familiar with refraction—the bending of light rays when they cross a transparent surface such as the front of a glass lens.

Eileen Reeves, author of Galileo’s Glassworks, on the other hand, surmises that Galileo may have erroneously assumed that the spyglass involved a lens-mirror combination because his friend Paolo Sarpi had unearthed some news about a so-called “French mirror.”

Reeves recounts an amusing tale that in late 1608 a scathing pamphlet describing the alleged sexual misdeeds of the Society of Jesus entitled Discoverie of the Most Secret and Subtile Practices of the Jesuits”, was published in Latin and then promptly translated into five other languages. This bawdy pamphlet happened to include also “a revelation about an optical device owned by the French King Henri IV’s confessor, Father Pierre Coton.”

“The Jesuits them-selves brag that hee hath a looking glasse of Astrology [speculum constellatum], wherein he made the King to see plainly what-soever his Majestie desired to know, and that there is nothing so secret, nor any thing propounded in the privy councells of other Monarkes, which may not be seene or discovered by the meanes of the of this celestial or rather devilish glasse.”

Even before this publication, the Jesuits had already been satirically portrayed as colonizers of the moon “almost all of whom have fox tails attached to their belts, along with concave mirrors, with which they see what is done in the world and dazzle the eyes of those who look at them.” Reeves thus concludes that the conventional account of Galileo’s belated awareness of the telescope—that he heard nothing of it for eight or nine months after its emergence in The Hague- should be reexamined in light of the news concerning the mirror in Paris.

It remains a matter of speculation that Galileo was seriously sidetracked by these far-fetched and fanciful rumors, however it is fun to imagine that if his investigations had taken him to experiment with reflective mirrors instead of refractive lenses, perhaps he would have discovered the Newtonian telescope long before Newton!

In next month’s podcast we will learn how Galileo rapidly improved upon the Dutch version of the spyglass and how it became to be known as the “telescope.”

End of podcast:

365 Days of Astronomy
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