QQ2 CONVERSION OF RELIEF BY INVERTED VISION. 



used by the mind itself to produce the illusion. In the normal case, however, 

 where the cavity or convexity is shadowless, and upon an extended surface, and 

 where inverted vision is used, the conversion of Form depends solely on the illu- 

 sion, which it is impossible to resist, that the side of the cavity or elevation next 

 the eye is actually farthest from it an illusion not produced by inversion, but by 

 a false judgment respecting the position of the surface on which the form is 

 placed. 



ST LEONARD'S COLLEGE, ST ANDREWS, 

 May 4. 1844. 



