528 Scientific Proceedings, Royal Dublin Society. 



other members of the Irish Lights Board, and looked at it from 

 SalthiU. 



In parenthesis, I may here say it was this light, thus tested 

 practically and commended by the high authorities I have named, 

 that the Trinity House refused to try at the South Foreland 

 experiments, which experiments were instituted by the Board of 

 Trade for the express purpose of testing all lighthouse lights. 



In the year 1885 a question arose as to whether it would be 

 advisable to adopt this double quadriform light at Tory Island 

 lighthouse, then being reconstructed ; but Sir Robert Ball, who is 

 scientific adviser to the Commissioners of Irish Lights, pointed out 

 that the light having but two faces would not be suitable for that 

 lighthouse, which it was intended should be a group-flashing light 

 having a considerable number of flashes. I will presently explain 

 this point ; but, meanwhile, perhaps you will allow me briefly to 

 refer to what teas done at Tory Island. 



In the year 1872, in this Lecture Theatre, and in subsequent 

 papers read to the British Association and the Institute of Civil 

 Engineers, and on other occasions, I strongly urged that in order 

 to take advantage of the full light to be derived from the large gas- 

 burners then introduced, large long-focus lenses should be con- 

 structed specially to suit them, and thus prevent the waste of the 

 light caused by its having to be transmitted by the small lenses 

 designed by Fresnel for the lamps of much less diameter used in 

 his time ; and that till this was done the full benefit of the gas 

 system would not be obtained. It was not until the year 1885, 

 through the influence of Messrs. Stevenson, the eminent engineers 

 of the Scottish Lighthouse Board, that the use of one of these 

 lenses, as an experiment, was at last sanctioned by the Board of 

 Trade. It gratified me exceedingly to learn that the trial of that 

 lens had resulted satisfactorily, as I had so long before and so 

 frequently predicted. I pressed the Commissioners of Irish Lights 

 to adopt these lenses at Tory Island, certain of the additional illu- 

 mination they would give (as, indeed, the result has amply proved), 

 and feeling confident that the further step of doubling the great 

 light from these lenses, by the adoption of the double quadriform 

 arrangement, would follow when sufficient attention had been 

 given to the subject. 



To return to the construction of the double quadriform as 



