 This device was attached to a wall of the camera obscura (EF).This universal joint mechanism was later called a scioptric ball.In his 1637 book "Dioptrique" French philosopher, mathematician and scientist René Descartes suggested placing an eye of a recently dead man (or if a dead man was unavailable, the eye of an ox) into an opening in a darkened room and scraping away the flesh at the back until one could see the inverted image formed on the retina.