76 Scientific Proceedings, Royal Dublin Society. 



a beam of eight-fold the intensity of a single light is obtained 

 from the Double Quadriform. 1 An ingenious contrivance allows 

 the whole arrangement to be rotated without disturbing the gas 

 supply ; thus the entire horizon can be successively illuminated with 

 a beam of light of surpassing power. 



The Commissioners of Irish Lights have for some months past 

 been testing this new Double Quadriform light, which they have 

 had erected in an experimental house at Howth Head, some 100 

 . yards distant from the Bailey lighthouse, the well-known powerful 

 first-order light at the entrance to Dublin Bay. The Bailey, it 

 may be mentioned, is also a gas lighthouse that can, by the addition 

 of concentric rings of burners, be rapidly raised when fog prevails 

 from 28 to 48, 68, 88, or 108 jets. Alongside the Bailey light is a 

 powerful siren trumpet, driven by a gas-engine, and blown by com- 

 pressed air at minute intervals during heavy fogs. 



It so happened that on both the evenings when I had arranged 

 to observe the new light a fog had settled over the Bay of Dublin. 

 My position of observation was near my own house at Monkstown, 

 where, in clear weather, an uninterrupted view over the bay can be 

 obtained, my standpoint being distant six miles, as the crow flies, 

 from the experimental lighthouse. 



Evening of November 18. — Owing to the intervening fog no 

 trace of the Bailey light could be seen, though its position was 

 well known. The first experiment was the trial [of a series of gas- 

 jets fed with " albo-carbon " vapour and oxygen, placed in the 

 focus of a first-order annular lens, such as is used for revolving 

 lights. Brilliant as was the light so produced, it was completely 

 cut off by the fog before it reached me, though the beam was di- 

 rected on to the position I occupied. "With a large opera glass I 

 was however just able to make out the light, and saw also the 

 Bailey near it, as a fainter speck of light. Suddenly, at the pre- 

 arranged time, a clear well-defined pillar of light sprung into view, 

 easily visible to the naked eye, and appearing as a large distinct light 

 through the glass. This was the Double Quadriform. In ten 

 minutes, as had been arranged, that was extinguished : complete 

 darkness again covered the horizon. With great difficulty, and 



The South Foreland experiments were made with a light of half this power. 



