AN 



; .. ESSAY 't'' 



UPON 



SINGLE VISION WITH TWO EYES. 



PART I. 



Of the different Opinions concerning single Vision with 

 two Eyes ; and principally of those of Dr. Smith and 

 Dr. Reid. 



1 HE end I have chiefly in view, in this Essay, 

 being to offer a new solution of the question, 

 why objects are perceived single with two eyes, 

 I think it incumbent upon me, in the first 

 place, to show, that none of the opinions I have 

 met with upon this subject, can be admitted as 

 just. 



These opinions, or such of them, at least, as 

 have gained any considerable reputation, may 

 be reduced into two classes. The first com- 

 prehends those of Galen, Alhazen, Rohault, 

 Dr. Briggs, and Sir Isaac Newton, all of whom 

 have regarded the question I have mentioned 



