A Jenkins Prismatic disc (1924) sold this afternoon on ebay along with a neon tube etc. The prismatic disc is on the ebay auction 4th and 6th picture.
http://www.ebay.com/itm/PRE-1935-TEL...vip=true&rt=nc
A set of prismatic discs below which are displayed at the Henry Ford Museum.
http://www.madehow.com/images/hpm_00..._0_img0173.jpg
I don't know if I'll ever make it to the Ford Museum so I may never see one live.