LANTERNS. 



15 



All the rays which will fall upon the object will be in- 

 cluded in the angle b a c. Interpose the lens de be- 

 tween the light and the object, and all the rays 

 included in the much greater angle d a e will now 

 fall upon b r, and it will be much brighter. There is 

 always another lens, and sometimes two, called the 

 objective^ in front of the lantern, to give definition to the 



picture. All the 

 essential parts 

 of a lantern are 

 shown i n the 

 accompanying 

 picture : — a \s 

 the source of 

 light inclosed in 

 the box b : d e, 

 ^^' ^' the lens for di- 



verting a greater number of light-rays, and called the 

 condenser; c is the objective ; and j, the screen to receive 

 the light. 



Fig, 6. 



