"Une Machine Infernale" (The engine), no date, E.H. Éditeur, Paris. (The images are colored on the back so when held to the light there are red fire sparks and glowing eyes.)
Viewing instruction: Scroll your browser window so that both images are visible (the image for the right eye is to the left and vice versa). Look at them at arm's length or more. Cross your eyes slowly until the images merge into one clear image in the middle and two other images on the sides. Give your eyes some time to adjust. The middle image should appear with plasticity and depth. For better viewing you may cover the side images with your hands. WARNING: Don't do this for too long, it is very tiresome for the eyes. Make sure that the distance to your screen is at least arm's length. If you increase the distance, the viewing gets easier.
About 3D images