274 hecext trogress of the theory of vision. 



that this conception of locality is innate ; and that im- 

 pressions derived from external objects are transmitted of 

 themselves to corresponding local positions in the image 

 produced in tli^ sensitive organ. We may describe this as 

 the Innate or Intuitive Theory of conceptions of Space. 

 It obviously cuts short all further enquiry into the origin 

 of these conceptions, since it regards them as some- 

 thing original, inborn, and incapable of further explana- 

 tion. 



The opposing view was put forth in a more general 

 form by the early English philosophers of the sensational 

 school — by Molyneux,^ Locke, and Jurin.^ Its applica- 

 tion to special physiological problems has only become 

 possible in very modern times, particularly since we have 

 gained more accurate knowledge of the movements of the 

 eye. The invention of the stereoscope by Wheatstone 

 (p. 284) made the difficulties and imperfections of the 

 Innate Theory of sight much more obvious than before, 

 and led to another solution which approached much 

 nearer to the older view, and which we will call the 

 Empirical Theory of Vision. This assumes that none of 

 our sensations give us anything more than ' signs ' for ex- 

 ternal objects and movements, and that we can only learn 

 how to interpret these signs by means of experience and 

 practice. For example, the conception of differences in 

 locality can only be attained by means of movement, and, 

 in the field of vision, depends upon our experience of the 

 movements of the eye. Of course, this Empirical Theory 

 must assume a difference between the sensations of 

 various parts of the retina, depending upon their local 



» William Molyneux, author of Dioptrica Xova, was born in Dublin, 1656, 

 and died in the same city, 1698. 



2 James Jurin, M.D., Sec. R. S., physician to Guy's Hospital, and Presi- 

 dent of the Royal Collfge of Physicians, was born in 1684, and died in 1760. 

 Beside works on the Contraction of the Heart, on Vis viva, &c., he pub- 

 lished, in 17.38, a treatise on District and Indistinct Vision. — Ts. 



