All medievalists are familiar with the image of the Wheel of Fortune that adorns many a manuscript page as well as several of the covers of modern editions of certain medieval texts. For example, see this image from the first folio of British Library, MS Royal 20 C IV, which contains a French translation of Boccaccio's De casibus virorum illustrium (On the Fates of Famous Men), itself an influential model for an entire genre of writing chronicling the downfalls of great men, including Chaucer's own "Monk's Tale." As Fortune spins her wheel, she elevates some men from a lowly state to greatness, but also causes others already in prosperity and lofty positions to tumble down -- sometimes on multiple occasions in one lifetime. I'm especially fond of this particular illumination because of the way the artist depicts the unfortunate souls on the wrong side of the wheel physically tumbling out of their now upturned chairs.
If you recall, Chaucer depicts the mechanism by which fame both good and bad is spread across the world as a horn blown by the god of winds, Aeolus, and borne by his henchman Triton; one horn creates good fame, named "Clere Laude," and another black trumpet called "Sklaundre" spreads ill fame. Triton, of course, is the classical sea god that appears as an object of desire along with his most famous attribute, the horn, in Wordsworth's famous sonnet: "...Or hear old Triton blow his wreathèd horn." While Chaucer does not make it clear that we should picture "Clere Laude" as the conventional conch shell of Triton's iconography, I like to think that it is, and I can attest that blowing a good long blast on a conch again helps make the sometimes distant images in these poems very immediate. For instance, the arresting image AND sound of someone blowing on a conch horn makes for a useful prologue to discussing the current of near synesthesia in The House of Fame, which reaches its high point in the description of the "blake trumpe of bras" Sklaundre. The sound of bad fame is first reified as a physical object, a cannonball (1643-1644), and then accompanied by a dark but multicolored smoke that both defies the laws of physics and offends the nostrils: "And hyt stank as the pit of helle" (1654). By the way, I happen to teach on the 7th floor of our library, the exclusive territory of Notre Dame's internationally renowned Medieval Institute, whereas I'm just a humble member of the humble English department myself -- I hope the conch hasn't earned me too much "bad fame" among the MI crowd.
And then there's my cheap reproduction astrolabe, that medieval combination slide rule and star chart. A long discussion of the astrolabe is perhaps more suitable for a course on The Canterbury Tales, with its cornucopia of astrological references -- or, I suppose, if it exists anywhere, a course on Chaucer's own piece of technical writing The Treatise on the Astrolabe.