SINGLE VISION. 59 



therefore be now seen in different directions by 

 the two eyes, and consequently double. An 

 experiment with a contrary event will confirm 

 this explanation, and likewise show more 

 clearly, in what I differ from those who have 

 endeavoured to account for the same fact. 

 Both eyes being open, let one of them be 

 pushed from its situation, and let two similar 

 objects, such as two pieces of money of the 

 same metal and stamp, be afterward so placed, 

 that one shall He in each optic axis ; these two 

 objects will now appear to be one, and the 

 object so compounded will be seen in the place, 

 to which the undisturbed eye refers the truly 

 single object lying in its axis. 



Another inference from this doctrine is, that, 

 if the eyes are in any very unusual position 

 with respect to each other from the action of 

 their own muscles, as in persons who squint, 

 two objects placed in the optic axes, one in 

 each, will not appear as one object ; for each 

 will be seen in the direction, which is de- 

 termined by the state of action in the muscles 

 of the eye, upon whose retina its picture falls ; 

 and as this state, in one eye, does not corre- 

 spond with that in the other, the directions 

 cannot coincide. This conclusion is verified 

 by the result of an experiment of Dr. Reid 

 upon a person, affected with strabismus, and 



