REFRACTING TELESCOPES. 



531 



5 cm focal length is used as the eye-piece 0, and the tube with the 

 object glass is moved until the distance of the lens from the end of 

 the board B is about 15 cm . 



For the terrestrial telescope the same lens forms the eye-piece, and 

 the convex lens of 3 cm focal length serves for the lens u required for 

 inverting the primary image. The cork frames for these two lenses 



D 



LIRI? A If. Y 



UNIVKUSITY OI 



CALIFORNIA. 



I*""- = 



FIG. 290 (A, B, C, an. proj., | real size ; D, % real size}. 



are fixed 9 cm from one another at the opposite ends of 6, and the 

 object glass will have to be moved to near the end of B. 



For the Galilean telescope 0, the concave lens of 5 cm focal length 

 is used as the eye-piece, and the object lens will have to be placed 

 at about the middle of B. 



The inverted real image produced by the object glass of the 

 astronomical telescope is at a in fig. A, where the three flames, OB. 

 account of the small size of the figure, are indicated by dots. The 



M M 2 



