Even though the psychologist may show that stroboscopic motion is produced without any intermediate stimulus between the extreme positions, and even that the luminous line A does not travel through the space which separates it from, that no light is perceived between A and during stroboscopic motion, and, in fact, that I do not see the pencil or the workman's arm between the two extreme positions, the fact remains that in some way or other the moving body must have been present at each point of the journey for movement to be apparent, and though it is not perceptibly present in all these places, it is thought of as there.