18 



THE BOOK OF THE LANTERN. 



we require to show in an enlarged form. is the objective 

 lens by which this enlargement is to be brought about ; 

 the sheet or screen upon which the picture is projected 

 being supposed to be far away to the right. With such an 

 arrangement of parts what should we see on that screen ? 

 In the first place we should have but a very feeble light, 

 for as will be seen by reference to the diagram, most of 

 the luminous rays are wasted altogether, only the cen- 

 tral ones proceeding through the lens 0. It will be 

 seen also that these rays go through the central portion 

 of the picture only, and that therefore only this part 

 can be projected on to the distant screen. So that as a 

 result of our first efforts at lantern projection, we get an 

 indistinct and badly-lighted portion of a picture presented 

 to us. How can we remedy this state of things ? Ob- 

 viously, the thing to be done is to cause more of the rays 

 from our light source to be utilised, and this can be brought 

 about by placing between that light and the picture a lens 

 which shall condense the light upon that picture, and which 

 is therefore known as the condenser. 



In fig. 11 we see a repetition of the diagram, fig. 10, with 



FIG. 11. 



the addition of a condenser, shown in this case, for the 

 sake of simplicity, as a single lens. Referring once more 



