The Stereoscopic Viewer and Cards an example of high Victorian engineering.
It shows an understanding of how the eye and brain work together to bring our world into three dimensions.
They were used mainly for pleasure, a sort of parlor room traveling. Safely bringing the exotic to the family. Showing the scale of the British empire. They were also used in the 2nd world war to give greater clarity to reconnoissance photos.
I love these cards especially those showing water. I have a few of Niagara Falls seemingly frozen in time, the huge physical power of the falls hanging there.
My absolute favorite is a image of the moon, through the viewer it shown as a orb, the curve of the surface is so exciting just like looking at the actual moon with binoculars.
The card in the viewer in the photo is of the Venus di Milo in the Louvre Museum Paris