LECT, XX. 



Front View of Wheatstone's Stereoscope. 



A A'. Two plain mirrors, whose backs form an angle of 90 with each other. 



B. Upright, against which the common edge of the mirrors is fixed. 

 C C'. Two drawings which slide in grooves made in the pannels D D'. 

 The observer must place his eyes as near as possible to the mirrors, the right eye 

 before the right hand mirror, and the left eye before the left-hand mirror. 



Fig. 35. 



Plan of Wheatslone's Sterescope. 

 (The letters refer to the same object as in the preceding figure.) 



Wheatstone has given the name of stereoscope to the 

 instrument by the aid of which this illusion is produced. 



