"The stereoscope as a means of representation was inherently obscene in the most literal sense.
...The very functioning of the stereoscope depended...on the absence of any mediation between the eye and image.
It is no coincidence that the stereoscope became increasingly synonymous with erotic and pornographic imagery in the course of the 19th century.
Some have speculated that the very close association of the stereoscope with pornography was in part responsible for its social demise as a mode of visual consumption."