For the Ferroequinologists
Directors of the Union Pacific Railroad celebrate reaching the 100th Meridian, October 1866. According to a Union Pacific website, this milestone guaranteed the railroad the irrevocable right to continue westward, as stipulated in the Pacific Railway Act of 1862. You can just make out the letters I and D on the side of the tender, so I believe the locomotive is “Idaho,” built in April 1866 at Schenectady. Library of Congress image.
Get out your red/cyan 3D glasses, y’all.
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Dead Confederates, A Civil War Era Blog 
Can’t you hand out a Holmes stereoscope to each of us so we could fully appreciate the 3D image? 😉
There is an alternative does not require a special viewer or red/cyan glasses. It involves making an animated GIF that switches many times per second between the two images that make up the stereoview. The brain cannot process those quickly enough to distinguish them as two different images, and so it creates a crude three-dimensional effect without any additional viewer. I generally do not use it, however, because I’m concerned flashing image may cause problems for folks with a specific condition, that it can trigger a seizure.