282 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK HI. 



seem to come from the same point in space ; they will be depicted 

 on the retina of each eye, as would happen in the case of a real 

 object. Now, what is required to produce complete identity between 



the phenomena of vision in the case of the real object in relief, and 

 the same object in a picture ? This, that the two separate views be 

 precisely those received by each eye individually examining them 



