WHEATSTONE'S REFLECTING STEREOSCOPE. 



325 



observer's right hand appearing to be the image's left, and so on. 

 By holding a right-angled glass prism between the eye and any 

 object in the position indicated by fig. 168, rays from an object, ab, 



Fig. 166. Wheatstone's Reflecting Stereoscope. 



incident on one face of the prism are refracted to the back of the 

 prism, where they are totally internally 

 reflected to the other face, whence they are 

 again refracted to the eye at c, which ac- 

 cordingly perceives an image at de reversed 

 relatively to the object as any other reflected 

 image would be (i.e., as regards right and 

 left, but not turned upside down). A pair 

 of such prisms, one for each eye, set in a 

 frame something like an opera-glass consti- 

 tutes the pseudoscope, which reverses every- 

 thing looked at. One effect of this is that, if a properly lighted 



Fig. 167. Reflecting 

 Stereoscope. 



