OX LIGHTHOUSE CHARACTERISTICS. 399 



in the time-keeping of flashing lights, even on 

 shore, the distinction between fifteen and twenty 

 seconds could scarcely be relied upon as given by 

 the mechanism ; and even if given trustworthily by 

 the mechanism, the distinction could only be 

 discovered by the sailor with certainty by the aid 

 of a chronometer, the use of which is out of the 

 question as a practical means for recognising a 

 light when seen. To give sufficient distinction 

 between these two lights, therefore, it was found 

 necessary to use colour; the East Goodwin was 

 made green, the Gull Stream white. Again, the St. 

 Agnes Light, Scilly, and the light on the Wolf Rock 

 two far outlying lights, about twenty miles asunder, 

 are each of them of half a minute period from flash 

 to flash, and the sole distinction between them is 

 that the flashes of the Wolf Light are alternately 

 white and red, while those of the St. Agnes' Light 

 are all white. 



The insufficiency of the distinction of flashing 

 lights, merely by length of period, had come to be 

 felt so strongly that a very important fresh dis- 

 tinction was introduced in 1875, in the lightship 



