306 MOVEMENT 



ingenious toy invented by Plateau at the beginning of 

 the present century, and to which he gave the name of 

 " Phenakistoscope." 



The original form of this instrument was a play- 

 thing which delighted us as children; it was destined, 



Fig. 202— Disc of a phenakistoscope, showing the different phases of movement of a 

 gull's wing. 



however, one day, to be used for more interesting 

 purposes. The phenakistoscope consists of the follow- 

 ing parts, a cardboard disc perforated at equal distances 

 round the periphery by small slits. One side of the 

 disc is blackened, and on the other a series of images 



