OX LIGHTHOUSE CHARACTERISTICS. 415 



urgent in the case of eclipsing lights as it is in the 

 case of flashing lights. A long period in the case 

 of a flashing light means a long period of darkness, 

 throughout which the light is lost sight of. The 

 inconvenience of a long period in an eclipsing light 

 is merely the length of time during which the sailor 

 may have to wait to know which light it is ; he 

 never loses sight of the light except for the two 

 or three seconds' duration of one of the eclipses. 

 But quickness of each group is just as important to 

 allow ready and sure identification of its character 

 as is the quickness of a group of flashes in the 

 group-flashing lights of which I have already 

 spoken. 



The important question is now to be met How 

 may eclipses be best arranged to give the requisite 

 number of characteristic distinctions, for the large 

 number of fixed lights on our coasts which need 

 distinction, with as little as may be of interference 

 with the valuable quality of fixity ? The answer, I 

 believe, is by groups of eclipses described as 

 follows : First one, two, three, or four very short 

 eclipses say of not more than one second each 



