Illusion Tops / Whirligigs is a set of 2 illusion tops. The black and white top is known as benham's wheel. It is an old optical illusion. As the top spins, you will see various colors, especially at slower speeds (Mostly faint reds and greens). However, the effect does not show up in the video and is only noticable in person. The red and blue top mixes colors while it spins to create various shades of purple. If you spin it under fluorescent lights or in front of a tv screen, the rings will seem to spin in opposite directions and some strobing will occur. The effects will also vary at different speeds. Some of the description text above is printed on the underside of each top. These tops were made by the company Toycrafter, which has gone out of business. When these are sold out, they will no longer be available. Diameter = 3 1/4 inches (80mm). Height = 1 1/2 inches (40mm).