Philosophical instruments were designed to examine phenomena experimentally, rather than by naturalistic observation alone. In the nineteenth century, some instruments were called philosophical toys because they provided popular amusement as well as experimental assistance. They were applied widely in natural philosophy, but attention here is directed particularly to manipulations of perceived space and time and their influence on art. One of the earliest instruments, which had a profound impact on art as well as science, was the camera obscura. It assisted image formation in art before it was applied as an analogy to the eye at the beginning of the seventeenth century. Later philosophical toys were used to address visual perception of motion and depth. Development was initially driven by the need for stimulus control so that the methods of physics could be applied to the study of perceptual phenomena. The principal instruments were invented in the first half of the nineteenth century, and they consisted of simple contrivances that manipulated time and space in ways that had not previously been appreciated. They included thaumatropes, phenakistoscopes, stroboscopes, anorthoscopes, stereoscopes, tachistoscopes, and chronoscopes. Several of these philosophical toys proved to be phenomenally popular, particularly when combined with photography.