Shattering crystal with crystal: Galileo's rhetoric, lenses, and the epistemology of metaphor.

The terms that Galileo's contemporaries used for lenses (cristallo/i, lente/i, and vetro/i) have often been treated, and even translated, interchangeably. In this article, we argue that Galileo used references to crystals as lenses to embed epistemological and cosmological arguments in the material object of the telescope. Across Galileo's correspondence and letters, the term crystal had many uses and meanings. As a substance, crystal was a form of raw material, but crystal was also a substance that was central to scholastic cosmology and an explanatory device on which scholastics relied to explain first the appearance of the new star of 1604 and then Galileo's new telescopic discoveries. When Galileo began using the word crystals as a synonym for lenses, he endowed the material of his instrument with cosmological arguments. Galileo's choice of language was deliberate and polemical, serving as a joke at the expense of scholastics and as a linguistic marker of social proximity to Galileo and his intellectual agenda, especially among the members of the Academy of the Lincei. Rhetorically and linguistically, Galileo chose to refer to his lenses as crystals both because of the material from which they were made and because in so doing he signaled the epistemological work that the lenses would perform. Ultimately, the crystal lenses in Galileo's telescope and writings shattered the crystalline spheres, replacing explanatory metaphors with a polemical emphasis on the material and empirical realities of objects.