Stereoscopic images from the village of St Nicolas, which, viewed through a device called a Stereoscope, gave the impression of a three dimensional scene. Most people can, with some practice and a little effort, view stereoscopic image pairs in 3D without the aid of a Stereoscope. However, the physiological depth cues resulting from the unnatural combination of eye convergence and focus required can cause headaches, eye strain and fatigue. And not to mention, leave viewers cross-eyed for hours. The Stereoscope was later replaced by the truly awesome View-Master.