

PART II. 



Of a new Theory respecting Visible Direction, and of' a 

 Solution hence derived of the Question, why Objects are 

 seen single with two Eyes. 



1 NOW proceed to offer a new opinion, why 

 objects are seen single with two eyes ; or in 

 other words, why they appear in the same place 

 to both, this being the light in which I view the 

 fact to be explained. 



In every part of natural philosophy, accidents 

 often lead to discoveries, which reason alone 

 might not easily have reached. Under this 

 cover I hope to shelter myself from the charge 

 of presumption, in venturing to give the solu- 

 tion of a problem, upon which the talents of 

 many persons of great learning and "genius have 

 been unsuccessfully employed ; for should I 

 prove more fortunate than such men have been, 

 this must be attributed to the knowledge of a 

 circumstance I observed by chance, in repeating 

 some very common experiments. 



The visible place of an object being com- 

 posed, as I have already several times remarked, 

 of its visible distance and visible direction, to 

 show how it may appear the same to both eyes, 

 it will be necessary to explain, in what manner 



