crown of thirteen rings of glass, 

 forming by their union a hollow cage, 

 composed of polished glass, lO feet 

 high and 6 feet in diameter. I know 

 of no work of art more beautifully 

 creditable to the boldness, ardor, in- 

 telligence, and zeal of the artist." 



With the most complete lenses 

 about 60 per cent of the light is 

 rendered useful, the balance being 

 lost at the top and bottom and by 

 absorption of the glass of the lens 

 and the lantern. 



The first lens in the United States 

 was installed at Navesink light in 

 1 841. The largest lens in this service 

 is that at Makapuu Point light, Ha- 

 waii, which is S-yi feet in diameter. 

 The introduction of more powerful 

 illuminants and quick-flashing lights, 

 with lenses concentrating more of 

 the light, has rendered large diameter 

 lenses unnecessary (see page 41). 



INGENIOUS METHODS TO DISTINGUISH 

 LIGHTS FROM EACH OTHER 



It is important that lights be so 

 distinguished from each other as to 

 avoid the possibility of the mariner 

 mistaking one for another. To this 

 end lights are distinguished by their 

 number, color, intensity, or time of 

 visibility. Before the introduction of 

 flashing or occulting lights, in a few 

 cases two or three light-towers were 

 built close together to give a dis- 

 tinctive combination, an example be- 

 ing the two lighthouses on Thatcher 

 Island, Cape Ann. This is an expen- 

 sive method not now employed for new 

 lighthouse work. 



Color distinctions, especially red, have 

 been widely used, but arc not suitable 

 exceprt for minor lights because of the 

 great loss of power; with the best color, 

 red, the loss is about 60 per cent. For 

 lights to be seen at close range, two lights 

 are sometimes shown, one vertically 

 above the other. 



\\'ith the systems now available of 

 flashing and occulting lights, it is possi- 

 ble to obtain a great variety of clearly 

 distinguishable characteristics. The first 

 revolving light was installed in Sweden 

 in 1763. The earlier slow revolving 

 lights are now generally superseded by 

 lights giving a flash or various combina- 

 tions of flashes at shorter intervals, or 



£iB^!^ms?sssk<z ^''-»K:--ys^-LM- 



.«i-jr-a 



AN ACETYLENE GAS LIGHT^ THE FAIRPORT 

 W^EST PIER LIGHT, OHIO 

 Gas tanks at base; light automatically occulting 

 every two seconds. Sun valve to the left of lan- 

 tern automatically cuts off the light while the 

 sun shines. 



lights showing continuously except for 

 short occultations. Quick-flashing lights 

 were first introduced in France about 

 1892. 



The most powerful flashing lights are 

 arranged to have the entire lens revolve, 

 the beam from each panel of the lens 

 appearing as a flash as it sweeps past the 

 observer. To obtain rapid and smooth 

 revolution, the lense is mounted on a 

 mercury float, and a lens weighing, with 

 fittings, as much as 7 tons may make a 

 complete revolution in 30 seconds. 



A recent examj^le is the lens for Kila- 

 uea light station. Hawaiian Islands, built 

 in France and co.sting about $12,000, in- 

 cluding import duty. The moving part 

 weighs nearly 4 tons and turns on a mer- 

 cury float, making a complete revolution 



37 



