3D photography or stereoscopic photography is the art of capturing and displaying two slightly offset photographs to create three-dimensional images. The 3D effect works because of a principle called stereopsis. Each eye is in a different location, and as a result, it sees a slightly different image.
Extraction from The American Journal of Photography by Various
“Of late, there is quite a revival in this branch of our art-science, several English and many foreign amateurs having been working with twin lenses during the last and present seasons. The Belgian Bulletin has an article on the subject, and the last technical meeting of the Photographic Society was devoted to it. Although Wheatstone announced the instrument in 1838, it was not until photography had come to his aid by furnishing satisfactory diagrams, and Brewster had popularized the matter by the invention of the lenticular stereoscope, that much progress was made; then Wheatstone gave his Bakerian lecture on January 15th, 1852, to put the finishing touch to this important branch of scientific work. The earlier attempts failed by reason of employing too wide an angle.”
Source: Project Gutenberg
The American Journal of Photography by Various