REFRACTION OF LIGHT. 



323 



Fig. 263. 



therefore, of a concave lens is not real, but virtual, as is 

 the case with a convex mirror. 



Thus, in Fig. 263, 

 the parallel raj-s, a b 

 cde, etc., falling upoa 

 the double concave 

 lens, L L', are so re- 

 fracted in passing 

 through it, that they 

 are made to diverge, 

 as though proceeding 

 from the point F, be- 

 hind the lens. 



In a similar man- 

 ner convergent ray nre rendered less convergent, or even parallel. 

 Do convex ^82. Images are formed in the foci of con- 

 vex lenses in the same way as in the foci of 

 concave mirrors. 

 Thus, if we take a convex lens and place behind it, at a proper distance, a 

 s'lcet of paper, there will be depicted upon the pap r beautifully clear and 

 distinct images of all the objects in front of the lens, in an inverted position. 

 The manner in which they are formed is illustrated in Fig. 264:. 

 Thus, let A B 



convex 

 lenses jrive rise 

 to thfi forma- 

 tion f images? 



Dcscribfi the 

 formation of 

 ima'^es by the 

 convex lens. 



Fig. 2G4. 



represent an ob- 

 ject placed be- 

 fore a double 

 convex len.g, E F. The rays 

 proceeding from A, the top of 

 the object, will be converged 

 by the lens and brought to a 

 focus at D, where they will 

 form an image; the rays pro- 

 ceeding from B, the base of the object, will also be converged and brought 

 to a focus at G ; and so. each point of the object, A B, will have its corre- 

 sponding image between C D. In this way a complete image will be formed.. 



The image formed by a convex lens will ap- 

 pear inverted, because the rays of light from 

 the several points of the oliject cross each 

 other in proceeding to the corresponding points 

 of the image. 



Thus, in Fig. 264, the ray, A E, proceeding from the top of the object and 

 filling obliquely upon tlio lens, is refracted into tlie course E D, and in lika 

 manner the ray B F is refracted in the direction F C ; and as these rays cro33 



Why are the 

 Images formed 

 hy convex 



lenses invert- 

 ed? 



