ON LIGHTHOUSE CHARACTERISTICS. 393 



great deal of light was given with a moderate 

 consumption of fuel, took the place of the coal fires 

 on the cliffs. Then reflectors were introduced. A 

 great invention was made early this century, which 

 led to the now prevailing dioptric system. It is 

 perfectly clear that the great brilliance and success 

 in economizing the fuel of the flames in the light- 

 houses of the present day is directly due to the 

 invention of the dioptric system ; and has been 

 largely promoted by the great use made of it, and 

 the great improvements effected on it, by Messrs. 

 Stevenson, the engineers of Northern Lights. 

 Then came the question of how to economize light 

 when not wanted to show all round, as, for instance, 

 in the case of the Lamlash Light, which shows a 

 brilliant light seaward, and a moderately-bright light 

 over the Bay of Lamlash. The occulting light 

 shown by the Messrs. Stevenson in our present 

 Exhibition is a light fulfilling one of the conditions 

 of characteristic quality, with very perfect 

 economy of light. The very principle by \vhich 

 light was economized has given one of the first 

 lighthouse characteristics in the ordinary revolving 



