52 TRANSACTIONS. I9OI-2 



tor was the next progressive step, but the crowning improve- 

 ment in the illuminating apparatus of light houses was the 

 utilization by Fresnel of there fractive power of glass, when 

 cut into properly shaped lenses, to direct the light into paral- 

 lel beams. 



Since the days of Argand and Fresnel little has been 

 done to improve the theory of lighthouse illumination. 

 The principles adopted by them are still recognized as 

 accurate, and progress has been in the direction of increasing 

 the size and power of the apparatus, without departing from 

 their general principles. 



Spermaceti oil obtained from whales, seal oil and various 

 fish oils, as illuminants, gave place to Colza oil, a vegetable 

 product, and it, in turn, has been displaced by petroleum, a 

 much cheaper illuminant, and capable of producing a much 

 larg-er and more brilliant flame. 



The English lighthouses burn petroleum in lamps having 

 as many as ten concentric wicks, with an intensity of 2619 

 standard candles. 



Of late years many experiments have been made with a 

 view to replace oil by coal gas, acetylene gas and electric 

 light, but petroleum is still generally used. It has the advant- 

 age over other forms of illuminants of being cheap and 

 easily stored, and of giving a light with a clear yellow colour, 

 which, it is claimed, penetrates fog better than the whiter 

 lights obtained from more modern illuminants. In the en- 

 deavour to secure the best possible light producer many very 

 powerful lamps have been invented, including a gas burner 

 made by Mr. Wigham, of Dublin, containing 108 gas jets. 

 He has superposed three such burners in the foci of separate 

 lenses in a single lighthouse. The difficulty of using this 

 apparatus consists in the great heat evolved, as well as iii the 

 immense lantern required to contain the superposed lenses, 

 and to give sufficient air for and ventilation to the flames. 

 Mr. Wigham has lately utilized the Auer light principle in 

 his multiple jet gas burners, and must secure very great ilium- 



