VISION. 



813 



Outward and downward Eectus externus, rectus inferior, 

 obliquus superior. 



STEREOSCOPIC VISION". When two monocular pictures are placed 

 side by side, and viewed by the two eyes respectively through the 

 two halves of a convex lens, we have one form of the instrument 

 called the stereoscope. The most striking results are produced by 



Fig. 365. Loring's Ophthalmoscope. 



two photographs taken at the same time by two cameras, so placed 

 that their axes shall form the same angle with each other as that 

 which the axes of the two eyes would form when looking at the same 

 object. When we look at a solid object near by with both eyes, the 

 right eye sees farther round the object on the right side, and the 

 left eye farther round on the left side. These two slightly different 

 images, when compared in the mind, produce the perception of 



