The modern zoetrope, also known as the Wheel of Life, was invented in 1834 by British mathematician William George Horner. The device became popular in the 1860s, thanks to Milton Bradley who patented it in the United States. It is one of a range of optical toys that delighted and intrigued people in the second half of the nineteenth century. The illusion of movement that the zoetrope demonstrates is based on the principle of persistence of vision, where the eye will remember an image for a brief moment. As the zoetrope spins one glimpses a sequence of changing images through the slits on the drum, and they appear animated. This simple idea forms the basis of modern film technology.