Rings with a dis­creet dual pur­pose have been in use since before the com­mon era, when Han­ni­bal, fac­ing extra­di­tion, alleged­ly ingest­ed the poi­son he kept secret­ed behind a gem­stone on his fin­ger. (More recent­ly, poi­son rings gave rise to a pop­u­lar Game of Thrones fan the­o­ry…)

Vic­to­ri­ans pre­vent­ed their most close­ly kept secrets—illicit love let­ters, per­haps? Last wills and testaments?—from falling into the wrong hands by wear­ing the keys to the box­es con­tain­ing these items con­cealed in signet rings and oth­er state­ment-type pieces.

A tiny con­cealed blade could be lethal on the fin­ger of a skilled (and no doubt, beau­ti­ful) assas­sin. These days, they might be used to col­lect a bit of one’s attack­er’s DNA.

Enter the fic­tion­al world of James Bond, and you’ll find a num­ber of handy dandy spy rings includ­ing one that dou­bles as a cam­era, and anoth­er capa­ble of shat­ter­ing bul­let­proof glass with a sin­gle twist.

Armil­lary sphere rings like the ones in the British Muse­um’s col­lec­tion and the Swedish His­tor­i­cal Muse­um (top) serve a more benign pur­pose. Fold­ed togeth­er, the two-part out­er hoop and three inte­ri­or hoops give the illu­sion of a sim­ple gold band. Slipped off the wearer’s fin­ger, they can fan out into a phys­i­cal mod­el of celes­tial lon­gi­tude and lat­i­tude.

Art his­to­ri­an Jes­si­ca Stew­art writes that in the 17th cen­tu­ry, rings such as the above spec­i­men were “used by astronomers to study and make cal­cu­la­tions. These pieces of jew­el­ry were con­sid­ered tokens of knowl­edge. Inscrip­tions or zodi­ac sym­bols were often used as dec­o­ra­tive ele­ments on the bands.”

The armil­lary sphere rings in the British Museum’s col­lec­tion are made of a soft high-alloy gold.

Jew­el­ry-lov­ing mod­ern astronomers seek­ing an old school fin­ger-based cal­cu­la­tion tool that real­ly works can order armil­lary sphere rings from Brook­lyn-based design­er Black Adept.

Note: An ear­li­er ver­sion of this post appeared on our site in 2021.

**Relat­ed Con­tent: **

A 16th-Cen­tu­ry Astron­o­my Book Fea­tured “Ana­log Com­put­ers” to Cal­cu­late the Shape of the Moon, the Posi­tion of the Sun, and More

When Astronomer Johannes Kepler Wrote the First Work of Sci­ence Fic­tion, The Dream (1609)

The Rem­brandt Book Bracelet: Behold a Func­tion­al Bracelet Fea­tur­ing 1400 Rem­brandt Draw­ings

Behold the Astro­nom­icum Cae­sareum, “Per­haps the Most Beau­ti­ful Sci­en­tif­ic Book Ever Print­ed” (1540)

Ayun Hal­l­i­day is an author, illus­tra­tor, the­ater mak­er and Chief Pri­ma­tol­o­gist in* New York City.*