78 Scientific Proceedings, Royal Dublin Society. 



ficient depth and density to cut off a first-class light shining through 

 an annular lens at half the distance, and to quench the sound of a 

 fog-siren adjacent to the double quadriform. 



It would have been important to have made a comparative 

 experiment with a single electric light of similar intensity, having 

 its beam concentrated by a single annular lens. There were, 

 however, no means of trying this. The recent elaborate Board 

 of Trade investigation at South Foreland led the eminent men 

 of science who conducted the inquiry to the conclusion that the 

 electric light has a slightly greater penetrative power in fog than 

 the triform oil or quadriform gas-lamp with which it was com- 

 pared, the two latter being practically equal, light for light, in all 

 conditions of weather. 1 



Nevertheless, it is much to be desired that some representa- 

 tives of the Trinity Board, or of the Board of Trade, should, 

 whilst the double quadriform is in its present position, come over 

 to Dublin, and in foggy weather test a gas-light twice as powerful 

 as any they have yet tried, and under conditions exactly similar 

 to those which prevail in the practical use of the light at sea. 



No doubt, the cost of the double quadriform light is consider- 

 able, both as regards initial expense and consumption of gas. On 

 the other hand, it must be borne in mind that a powerful light of 

 this kind is only intended for the more important points on the 

 Coast, and it is only under exceptional conditions of fog that 

 the full consumption of gas need be resorted to. Moreover, as 

 Mr. Howard Grubb, F.E.S. (who, independently of myself, has 

 recently tested this new light), has remarked in his Eeport : — 

 " Economic considerations fade into insignificance before the one 

 broad fact that, when occasion does require a powerful light, this 

 arrangement of Mr. Wigham's gives the power of producing a 

 revolving light unequalled by any existing arrangement." 



1 These conclusions, however, seem to be contradicted by, at any rate, one observer 

 (p. 29 of the Report), who, after comparing the lights in " drizzling rain and dense 

 fog," remarks : "In honesty, I award B [that is, the quadiforni gas], the most points, 

 for I consider it the best light from first to last." 



