http://antiqueboxes.org/bramahs-challenge-lock/

https://artuk.org/discover/artworks/joseph-bramah-17481814-216153

https://medievaljourney.com/2014/11/05/bramah-secret-vintage-locks-and-keys/

http://antiqueboxes.org/bramahs-challenge-lock/

https://www.npg.org.uk/collections/search/portrait/mw00104/Key-to-engraving-after-Men-of-Science-Living-in-1807-