ON LIGHTHOUSE CHARACTERISTICS. 407 



II. FIXED LIGHTS. 



Of the 623 lights numbered in the " Admiralty 

 List of Lights for the British Islands for 1881," 490 

 are fixed, 112 are flashing, and 21 are occulting 

 (or "eclipsing," or "intermittent"); and similar 

 proportions are to be found in the official list of 

 lights for other parts of the world. Thus it 

 appears that fixed lights constitute the great 

 majority. The fixed light has a great advantage 

 in respect to practical usefulness over the flashing 

 light, in being always visible. The superior 

 brilliancy produced by optical condensation of the 

 revolving light is, in some respects, dearly bought 

 economy, when the great diminution of usefulness 

 to the sailor, in its comparatively long periods of 

 darkness, is taken into account. Theorists who 

 praise the revolving light unqualifiedly for its 

 superior penetrative power seem to forget the 

 counterpart in optics to the great principle in 

 dynamics that which is gained in power is lost in 

 speed : in flashing lights, what is gained in brilliancy 

 is lost in time of visibility. The painfully anxious 



