What is a Stanhope lens? Briefly, it's a tiny microscope that was invented by Charles, the third Earl of Stanhope It's made by using a tiny tube of glass with convex ends. The image to be viewed is put at one end of the glass tube and appears to be magnified when the device is held up to the eye.
Stanhope lenses were especially popular during the 19th century and put in all sorts of souvenirs and novelty items. They were popular to sell at religious pilgrimage sites as well. An image of the site would be put at the end of the tube and the whole thing would be set into the center of a rosary crucifix. I have another one that shows six views of Lourdes, France when you look into the viewer! It's amazing when you realize how tiny the viewing area is.