I'll. Ill] INTERPRETATION OF APPEARANCES 113 



eye sees the image. After one is nsed to the stereoscopic appear- 

 ance when seeing with both eyes he can tell instantly whether the 



FIG. 102. Greenough's Erecting Binocular Microscope. This consists of 

 tti'o microscope tubes mounted side by side. The oculars may be approximated 

 or separated for the eyes of different observers. The images are erected by the 

 Porro prisms in the large rounded part of the tube. (Zeiss' Catalog.) 



