INERTIA AS RELATED TO CONSCIOUSNESS 89 



the time of the application of the stimulus, post- 

 stimulant retinal functional inertia, in short." 



It is owing to this property of inertia in 

 the retino-cerebral protoplasm that the beautiful 

 modern illusions of movement in the devices known 

 as kinetoscope (bioscope, mutoscope, &c.) are due. 



The stimuli illuminated, instantaneously taken 

 photographs are presented in a series with a very 

 small time-interval between the various members : 

 the perceptions are not serial or disconnected, but, 

 as every one knows, are quite continuous, producing 

 the illusion of more or less smooth movement. 

 Thus one sees without a break, such movements as 

 those of horses galloping, fish swimming in the 

 aquarium, a train approaching or receding. (The 

 flashes that often mar the effect in photographic 

 views hastily prepared for public entertainments, 

 are not " flicker " in the physiological sense of 

 non-fused sensations, but are probably due to dust 

 on the films reflecting or scattering light.) 



The visual positive after-image is then a case 

 of post-stimulant activity of protoplasmic inertia. 

 All the cases of colour-mixture where, e.g., a sector of 

 red followed by one of blue whirled in front of the 

 eye gives rise to a purple, or where a disc half black 

 and half white produces grey, are all cases of per- 

 sistence of retinal impression or of after-images 

 katabolic psychic inertia. Sometimes the positive 

 image gives place to the negative and the negative 

 to the positive, and so on for some seconds in 

 alternating fashion : this phenomenon is quite 



