PARABOLIC REFLECTOR. 



183 



" CHAPTER XXI. 



THE most important object to be sought, after determin- 

 ing the most satisfactory method of creating a bright light 

 for light-house purposes, is, as has already been said, to de- 

 vise the best means of utilizing it when created by concen- 

 trating it in the direction where it is required. 



In former times this was done by reflectors alone, the 

 light being placed in the focus of what is called a parabolic 

 reflector, which is a reflector of such a form that it reflects 

 the light radiating from the focus within in a beam of par- 

 allel rays issuing through the opening in front. 



PARABOLIC REFLECTOR. 



This is shown clearly in the engraving, the black lines 

 representing the natural course of the rays, and the dotted 

 ones the lines into which they are turned by the reflector 

 and formed into a parallel beam. 



We see this arrangement in operation in the front of the 



