LANTERNS. 



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 c> 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 is 

 the source of 

 light inclosed in 

 the box b ; d e, 

 Fi ff- * the lens for di- 



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

 condenser; c is the objective ; and s y the screen to receive 

 the light. 



Fig. 6. 



