Viewing the Watkins Yosemite Stereographs in 3D
To view these stereographs in 3D, move a little back from your normal viewing distance and put your index finger in line with the line between the two pictures and about halfway between your eyes and the pictures. Then focus on your finger. If you're lucky, three images will appear and the center one will be in 3D. Don't get discouraged if this doesn't work; few people are able to do it easily.
You can also make a paper 3D viewer, but few people are able to make that work. Another option is to use a Loreo Lite viewer or Plastic Stereo Card Viewer (Lorgnette), available for purchase online at low cost (see related links). While you're perusing viewers, take a look at the new HD 3D TVs. Watkins would be amazed.