Zoetropical Motion Explained !
The images in the Zoetrope will rotate in the drum (or not) depending on the number of images in relation to the number of slots. The original Zoetrope invented by William Horner in 1834 had 13 slots as did the Zoetrope patented by Milton Bradley in 1867. Professor Hall's Handheld Zoetropes have the authentic 13 slots so that the reproductions of original strips and floors will behave as they were intended.
If you look at the Animated Zoetrope strips included with Professor Hall's Handheld Zoetrope, you can count the number of images and tell how each strip will behave. To be authentic, the Zoetrope should have 13 slots and this determines how the floors will act as well (Four Animated Zoetrope Floors are included with each Zoetrope). Remember that 13 is the largest Prime Number and while "Zoetrope" means "Wheel of Life" in Greek, as a result of the 13 slots, the Zoetrope was also called the "Devil's Wheel" in the 19th Century. If you have a Zoetrope already or want to make your own, please feel free to copy the Animated Zoetrope strips on this website, just remember that any number of slots other than 13 will make the images move differently than intended.
Rules of Zoetropical Motion
Same number of images as slots and the images will move in place but not rotate in the drum.
Fewer images than slots and the images will move in the opposite direction the drum spins.
More images than slots and the images will move in the same direction the drum spins.
The number of slots is the median number and the greater the difference between the images and slots, the more extreme the motion. In the case of the authentic 13 slot Zoetrope, 11 images will move faster than 12 images, 13 will not rotate and 14 images will move slowly.
A little Pre-Cinema History
The Zoetrope is the Third Optical Toy. The First Optical Toy being the Thaumatrope which was used by PM Roget to demonstrate the principle of "Persistence of Vision" in 1824. Spin a coin on edge on a counter and you will seem to see both sides at once. That is the idea of the Thaumatrope. The Second Optical Toy is the Phenakistascope. Plateau and Stampfer followed up on Faraday's experiments in 1832 to produce the Phenakistascope which uses slits around the edge of a disc to act as the slots in the Zoetrope. The viewer holds the spinning disc up to a mirror and looks through the back side of the disc to see the reflection of the moving images through the slits. Eadweard Muybridge used a Projection Phenakistoscope to first publically exhibit his photographic motion studies in 1879. In 1877, Reynaud invented his Praxinoscope which used mirrors in the center of a spinning drum to reflect images on a strip so that the moving images appear in a fixed area like a movie screen. There is no shortage of valuable information of the Internet regarding these and other important Cinema History inventions.