THE PRINCIPLES OF VISION 185 



focus. In this case the rays on the opposite side of the 

 lens, instead of converging, continue in a divergent 

 course. 



Fig. 42.— Virtual image of a concave lens: 0\ B' is the virtual image 

 of the candle; 0, B, erect and diminished in size, (de Schweinitz, "Dis- 

 eases of the Eye.") 



The virtual image, seen through a convex lens, is 

 magnified, while that seen through a concave lens is 

 reduced. 



Fig. 43-— Image formed by a convex lens: 0, B is the object; 0', B' is the 

 inverted image, (de Schweinitz, "Diseases of the Eye.") 



The image formed by a convex lens is inverted. This 

 is so with the unage formed upon the retina. (As an 

 example, look at the image on the ground-glass of a 

 camera.) Following the refraction of this image for- 



