546 



EFFECTS OF PERSISTENCE OF IMPRESSIONS. 



The persistence of impressions of light on the retina 

 may be used to make an object of which a series of 

 figures is drawn on cardboard appear as if it were in 

 motion. Look first at A in fig. 297, then for a very 

 short time at B, then at (7, and so on along the whole 

 The eye will very nearly receive the impression 



series. 



of a moving pendulum ; for it sees successively twelve 

 figures, each of which is very little different from the 



FIG. 297. 



next, so that the sudden transition from one to another 

 is not felt, but an impression is produced as if one and 

 the same object were gradually changing. By present- 

 ing the figures successively to the eye, as for instance 

 by drawing a strip of paper with the figures on it be- 

 fore the eye, the impression of motion is very im- 

 perfect ; care must be taken that each figure is seen 

 only in a definite place, and that its onward motion is 

 not perceived at all. This may be accomplished by 



