448 



LIGHTHOUSE ESTABLISHMENT, THE UNITED STATES. 



rock stations where there was a scarcity of 

 fresh water, and where fuel was difficult of 

 access. But it is now losing favor because of 

 its liability to accident and the difficulty of its 

 repair. 



The siren, originally invented by Cagniard de 

 La Tour, and used by physicists in comparing 

 sounds and in measuring the number of vibra- 

 tions in different musical notes, was largely 

 changed by A. & F. Brown, of the New York 

 City Progress Works, under the direction of 

 the Lighthouse Board, and adopted for use as 

 a fog-signal. It can be sounded with either 

 steam or compressed air driven through a fixed 

 flat disk, placed in the throat of a trumpet, to 

 which is attached the pipe conveying the mo- 

 tive power. The disk has from eight to twelve 

 radial slits. Back of the fixed disk is a revolv- 

 ing plate with a like number of similar open- 

 ings, which is rotated by power specially ar- 



ranged for that purpose. When the slits in the 

 revolving plate coincide with those in the fixed 

 disk, as they must, say twelve times in each rev- 

 olution, a jet of steam or air is forced through 

 each opening under great pressure into the 

 trumpet, and the interruption of these jets 

 causes the song of the siren. The rotating 

 plate is directly connected with and supported 

 by the shaft, which is so geared to a steam or 

 hot-air engine as to make 2,400 revolutions per 

 minute, and as each revolution allows the escape 

 and interruption of twelve jets through the 

 coinciding openings, there are 28,800 shrieks 

 given, creating, as the vibrations are taken up 

 by the trumpet, a condensed beam of sound of 

 great intensity and of surpassing power. 



The siren is used on shore, as shown in the 

 following cut, and on light-ships, as shown in 

 the cut of Pollock Eip Light- Ship, on page 450. 



The first-class steam siren, when working 



SIREN FOG-SIGNAL. 



with a pressure of seventy-two pounds of 

 steam, consumes about one hundred and eighty 

 pounds of coal and one hundred and twenty- 

 six gallons of water per hour, and can be heard 

 under usual circumstances at a distance of 

 twenty miles, and in still air thirty miles, even 

 in a dense fog. Its range of sound, however, 

 is not deemed of so much importance as its 

 quality and its power of domination over lo- 

 cal noises, such as that of the surf, the whis- 

 tling of the wind through a ship's rigging, that 

 of paddle-wheels, or the working of an engine. 

 This it has to such extent that it has been 

 well said that " its density, quality, pitch, and 

 penetration render it dominant over such 

 noises after all other signal sounds have suc- 

 cumbed." The committee sent in 1872 by 

 the British lighthouse establishment, Trinity 



House, to this country, headed by Sir Freder- 

 ick Arrow and Captain Webb, of H. M. Navy, 

 reported so favorably upon it that, since then, 

 " twentv-two sirens have been placed at the 

 most salient lighthouses on the British coasts, 

 and sixteen on lightships moored in positions 

 where a guiding signal is of the greatest ser- 

 vice to passing navigation. 1 ' While the siren 

 is the best fog-signal yet invented, it is also the 

 most expensive to build and to run, is the most 

 complicated in its parts, and requires more at- 

 tention and skill in its management than any 

 other signal, and is adapted only to such sta- 

 tions as are amply supplied with water and 

 have machine-shops in the vicinity where ne- 

 cessary repairs can be promptly made. 



The steam-whistle is largely used as a fog- 

 signal, and with satisfactory results, in places 



