LIGHT 



229 



pi' 



The compound microscope consists of a convex lens 

 (Figure 204) of short focal length, called the objective, and 

 a larger convex lens L called the eye- 

 piece. When the object MN is viewed, 

 an image is formed at mn. This image 

 is further magnified by the eyepiece so 

 that it appears as M'N'. 



The telescope is like the compound 

 microscope with this difference the ob- 

 ject lens is made large for collecting a 

 large amount of light (Figure 205). 



The camera is a light-proof box fitted 

 with convex lenses. Light enters the 

 camera through the lens, which produces 

 on a ground glass at the rear of the box 

 an inverted image of the objects within 

 the range of the lens (Figure 206). If a 



Mirror 



sensitized plate or film is substituted for FlG - 2 , 04 A/r r A Com " 



* . pound Microscope. 



the ground glass, a picture will be pro- 

 duced by the chemical action of the light on the plate 

 or film. This plate is now treated with a developing 

 fluid, which brings out a visible and permanent image 



Totheobjtci 



FIG. 205. Telescope Lenses. ' 



of the objects taken in the picture. The plate is now 

 called a negative, because the light and shade are 



