184 



THE SEA. 



rough brass on the landward side, to serve as a reflector. Such methods of lighting were 

 of course very deficient in power, and did not enable the mariner to distinguish one light 

 from another a point which is often of as much importance as the brilliancy of the light 

 itself. Prior to the invention of the Argand lamp (about 1784) the production of a 

 strong and brilliant light from a single source was scarcely possible, and even such a 

 lamp, by its unassisted powers, would not be of very great value in giving early notice 

 to the mariner of his approach to the coast, which ought to be the primary object of a 



FLOATING LIGHT LANTERN 



HOLOPHOTAL REVOLVING LIGHT. 

 (FIRST ORDER ) 



REVOLVING LIGHT APPARATUS. 

 (From Drawings supplied by Messrs. W. Wilkins & Co.) 



HOLOPHOTAL REVOLVING LIGHT. 

 (FOURTH ORDER.) 



lighthouse. As the rays of a luminous body proceed in all directions in straight lines, it 

 is obvious that in the case of a single lamp the mariner would derive benefit only from 

 that small portion of light which proceeded from the centre of the flame to his eye. The 

 other rays would proceed to other parts of the horizon, or escape upwards to the sky, or 

 downwards to the earth, and thus be of no value to him. By increasing the number of 

 burners a small portion of light from each burner would slightly increase the effective 

 action, but by far the greater portion of the light produced would escape uselessly above 

 and below the horizon and also at the back of each flame. Next, these defects were 

 remedied, and the efficiency of the light greatly increased, by placing behind each lamp 

 a reflector of such a form as to collect the rays that would otherwise be lost, and throw 

 them forward to the horizon. The adoption of such a method has led to what is called 

 the catoptric system of lights. 



