FUNCTION OF THE REFLECTOR. 185 



near and distant vessels ; and they must also diverge to a 

 considerable extent from side to side, so that they may 

 reach every ship, whatever may be the direction from which 

 she approaches the land. 



Reflectors are necessary for all that portion of the ra- 

 diance which would naturally proceed toward the land, for 

 it is only by reflection that light can be turned back direct- 

 ly from its course. 



For a long time reflectors alone were used for the man- 

 agement of the light in these cases. They only served the 

 purpose, of course, of intercepting and turning forward that 

 portion of the radiation which was emitted on the side op- 

 posite to that on which it was required. The light which 

 naturally went forward was left to pursue its own course 

 without modification. It could only be modified by the 

 use of lenses, and the difficulty of constructing lenses of a 

 sufficient size for the purpose was for a long time insur- 

 mountable. 



Contrivances for reflecting the light were, however, very 

 numerous, and some of them were very ingenious and very 

 complicated. 



The engraving on the following page represents a sys- 

 tem of reflectors devised to produce Avhat is called a flash- 

 ing light; for, in the case of beacon-lights that are not 

 many miles apart, the luminous effects must be made to 

 differ in some way, in order to prevent their being mis- 

 taken for each other. There are a great many ways of 

 making these variations. The light may be colored by be- 

 ing caused to pass through red, green, or blue glass. It 

 may be revolving or intermittent, or may be sent forth in 

 flashes. In the engraving the several reflectors have each 

 its own lamp, and they are arranged in sets of three (A, B, 

 C) upon a vertical axis, which is made to revolve by ap- 

 proximate machinery, as indicated by the pulley on the 



