ON LIGHTHOUSE CHARACTERISTICS. 395 



Arts, of 1 5th December last, on "Signalling by 

 means of Sound," gave an interesting and clear 

 description of the chief practical methods hitherto 

 in use for this exceedingly important addition to the 

 efficiency of lighthouses ; and I shall have occasion 

 to return to the subject of characteristic sounds in 

 relation to the several methods which have been 

 adopted to give characteristic qualities to the light 

 itself of a lighthouse. 



Setting aside colour now generally admitted to 

 be indefensible, as a distinction for lighthouse lights, 

 except in the proper use of it, which is to distinguish 

 different directions of the light by coloured sectors 

 to mark rocks or other dangers, or the safe limits 

 of navigable channels we find all the characteristic 

 qualities of lighthouses to come under one or other 

 of the following three descriptions : 



I. Flashing lights. 

 II. Fixed lights. 

 III. Occulting or eclipsing lights. 



The well-known name " Revolving lights " is 

 habitually limited to flashing lights ; but it is liable 

 to ambiguity, because the same revolving mechan- 



