A disc-shaped information carrier is described which contains spirally arranged image and/or sound signals coded in optical form. By recording the information in at least two spiral information tracks which may be separately read the total amount of utilizable information may be increased by a factor...http://www.google.com.au/patents/US3999009?utm_source=gb-gplus-sharePatent US3999009 - Apparatus for playing a transparent optically encoded multilayer information carrying disc
