"The phenakistoscope (also called phenakistiscope) was an early animation device, the predecessor of the zoetrope. It was invented in 1832 simultaneously by the Belgian Joseph Plateau and the Austrian Simon von Stampfer."
The beautiful blue and white example above is from the collection of the Ecole des Beaux Arts in Paris.
To find out how it actually worked I consulted bizarrelabs.com:
"It is basically a disc fixed at its center so that it can spin freely. Around the edges are regularly spaced slits, and in conjunction with each slit is an image drawn in sequential stages of movement. Like all of the circular animation devices that followed, the animation was drawn in a cycle of sequential movement; there was no beginning or end, but a continuous kinetic flow. The person using the device would hold it between them and a mirror, with the images facing the mirror. When the disc was spun, the images were viewed, reflected by the mirror, through the passing slits. The spaces between the slits let the eye and brain "soak in" the image so that persistence of vision could create the illusion of movement. And, because the slit was narrow, each individual image was seen only in one position and was not blurred."
Some of the other explanations I came across supplied "how-to-do-it" pictures, such as these:
And it was an encouraging surprise to discover that there are still individuals alive today who make phenakistoscopes for fun:
But most of the examples I found were vintage, preserved at universities or in museums:
Online samples are often animated to simulate the spinning of the disc, such as the Michael Jackson tribute phenakistoscope viewable here.