CHAP. II.] 



LIGHTHOUSES. 



225 



of equal power all round the horizon, while in order to intercept the 

 light above and below the refractor he had a series of zones of 

 silvered mirrors, suitably inclined so as to reflect horizontally; "or 

 again by a series of prisms in which the luminous rays undergo 

 total reflection. Figs. 156 and 157 illustrate the path of these rays 

 in each arrangement. 



So that reflection and refraction are equally employed in these 

 methods, which for this reason are named catadioptric light-houses. 



1 



FIG. 158.- Fixed li<;ht of the 

 lirst order and white light. 



Fresnel did not stop at these capital modifications ; he improved 

 the lamps, and with the assistance of Arago, introduced the 

 system of multiple burners invented by Eumford and success- 

 fully combined Carcel's system, giving to the light the greatest 

 possible intensity and regularity, valuable qualities in this kind of 

 application. 



A word now on the means used to vary the lights and to afford 

 mariners the advantage of recognizing the coasts wherever they 

 may be. 



