Mr. A. Claudet on Moving Photographic Figures. 275 



only two pictures to look at alternately, one with the right 

 and the other with the left eye, as with the instrument I have 

 constructed for my experiment. One of the pictures represents 

 the beginning of an action, and the other the end of the same 

 action. By moving the slide one way the right eye can see the 

 picture representing the figure in one position and the picture 

 showing the other position is invisible to the left eye. Now 

 by moving the slide the other way the left eye sees the figure 

 in the second position, and the first position is invisible to the 

 right eye. Now, although we have only seen the figure in two 

 extreme positions, one showing the beginning of the action and 

 the other its end, still we have had the illusion of having seen 

 the intermediate positions. 



This is fully illustrated by tbe pictures representing two 

 boxers. In one picture the arms and fists of one of the pugilists 

 are near his body, as if he were preparing to hit his opponent ; 

 and in the other picture they are extended in the act of striking 

 the blow. We have not seen the intermediate positions which 

 the boxer ought to have gradually assumed during the whole 

 act, but we know that they must have taken place, and our 

 mind completes the action. This mental perception is due to 

 the sensation which we expect from habit and judgment, and we 

 feel it as if it had been truly realized. 



Another curious phenomenon is elicited by the alternate vision 

 of the two eyes consecutively. We see the object without any 

 difference or interruption, whether it is by the right or by the 

 left eye. The ultimate sensation on the mind is the same from 

 whatever eye it has been carried to the sensorium of vision. 

 Whether the object be seen by the right or by the left eye, the 

 sensation is exactly the same, and we cannot even distinguish 

 which is the eye that has had the perception ; so that if, while 

 we have both eyes open, an object is passing before us, or if we 

 move the hand before the eyes in such a manner that it hides 

 alternately the vision of one and of the other eye, we do not 

 feel that the vision is passing from one eye to the other, and it 

 is impossible to know by which eye we have had the perception. 



This explains the reason why in the instrument I have con- 

 structed, which alternately shows a picture in one position to one 

 eye, and a different picture in another position to the other eye, 

 we have a single perception of an object in motion without being 

 conscious that the two actions have been consecutively and sepa- 

 rately perceived only by one eye at a time, and in turn by one 

 and then by the other. The result is an uninterrupted percep- 

 tion of an object in motion. 



Our sensation of vision is not in the eyes, but only in the 

 single sensorium of vision, to which both eyes convey their sepa- 



T2 



