CHAP. II.] 



LIGHT 110 USKS. 



227 



revolving lights, white, red, or green combined diversely with differ- 

 ent duration of flash. In the latter the lenticular apparatus is formed 

 by an octagonal drum composed generally of eight simple Echelon 

 lenses. The greater or less rapid motion of the system gives place to a 



Fio. ICO. Section of the lighthouse at Cordouan. 



FIG. 161.- 

 The lighthouse at New Caledonia, 



succession of appearances " flashes " and disappearances of different 

 durations. The colour of the lights is varied by using coloured glasses 

 placed in front of the lenses. Fig. 159 gives an idea how the 



Q 2 



