SINGLE VISION. 15 



Having now said what, I hope, will be 

 thought sufficient to show, that the reason given 

 by Dr. Smith, for our seeing objects single with 

 both eyes, is neither grounded on well-attested 

 facts, nor adequate to the explanation of the 

 phenomena observed, I pass to the examination 

 of the opinion of Dr. Reid. 



As this neither rests upon nor includes any 

 new fact in vision, I need only mention, in 

 order to give an account of it*, that its author 

 maintains with Dr. Smith, that an object is seen 

 in the same place with both eyes, and conse- 

 quently single, when its pictures fall upon the 

 centres of the retinas, or upon points in them, 

 which are similarly situated with respect to the 

 centres ; but differs from him in this, that he 

 makes the property to be original, by which 

 any two places in those membranes exhibit only 

 one object, while Dr. Smith derives it altoge- 

 ther from custom f. 



In my examination of the opinion of Dr. 



* Inquiry into the Human Mind, c. vi. sect. 13. 



f They differ also with respect to the meaning of a term -, 

 Dr. Smith calling corresponding points, such as have the posi- 

 tion just mentioned, whether they represent objects single or 

 not j whereas Dr. Reid says, that those points correspond, 

 whatever their position may be, which represent objects 

 single 5 and he appears to me not always to attend to the 

 double use of the same term, when he speaks of the opinions 

 of Dr. Smith. 



