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SIGNAL LAKTKBN. 



looked around at the vast number of angular rings of glass 

 that is, rings angular in section and prisms, and groups 

 of lenses and reflectors, he was sometimes utterly bewil- 

 dered with the intricacy of the system, and almost dazzled 

 by the brilliancy of the effect produced by so much pol- 

 ished glass, even in the daytime, when the lamps were not 

 lighted. 



He found that not only lenses, modified as above de- 

 scribed, were used, but prisms of the same annular form, 

 placed above and below the limits of the lenses, were em- 

 ployed to bring down into parallelism rays which would 

 otherwise have passed out of range. Ho\v this is done will 



