SENSE ORGANS. 



H5 



any object fall on corresponding points, then the external 

 images are thrown to the same place and are superposed 

 and seen single, but when the two retinal images of an 

 object fall on non-corresponding points then the external 



Fig. 91. 



images are thrown to different places and are seen double. 

 Now it is at once seen why we see single what we look 

 at ; for then the axes of the two eyeballs are converged 

 on the object and the images fall on the central spots 

 or fovese, and these are par excellence corresponding 



