ON LIGHTHOUSE CHARACTERISTICS. 391 



being known is not enough. The question to be 

 considered is how to know one light from another 

 how to know a light descried just above the 

 horizon, and dipping now below the horizon, lost 

 sight of for a quarter of a minute, again seen, lost 

 for a little time, and again seen continuously to 

 recognise it with certainty, and without loss of time, 

 in such circumstances. The Holywood Bank Light 

 in Belfast Lough, the leading light for vessels enter- 

 ing the Lough, is so recognised, being a short-short- 

 long eclipsing light. The Copeland Light off the 

 south entrance of Belfast Lough is not recognisable 

 by any distinguishing characteristic, being merely a 

 fixed light. It has, however, I am informed, been 

 determined by the Commissioners of Irish Lights to 

 alter it, and give it a distinctive character. I take 

 those two cases because, when a celebrated 

 lighthouse engineer was with me on one occasion 

 in my yacht, approaching Belfast in the small hours 

 of a summer morning, we had just that experience 

 of them both. I said to him, " Look at that light 

 and tell me what it is ; is it a masthead light, or 

 what is it ?" He could not tell. It was the 



