January 5, 1894 ] 



SCIENCE 



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THE CEUISE OP THE CLOVER— FURTHER RE- 

 MARKS ON THE ABERRATIONS OF AUDIBILITY 

 OF FOG SIGNALS— THE METHODS USED.^ 



Br ARNOLD SURGES JOHNSON, WASHINGTON, D. C. 



It is now about a quarter of a century since Prof. 

 Joseph Henry, the first President of this society, com- 

 menced his investigation into the operations of the laws 

 of sound in connection with the fog signals used by the 

 Light House Board, of which board he was then the 

 scientific member. 



When I was made Chief Clerk of the Light House Board 

 in 1869 it became my duty, as well as a privilege which I 

 highly prized, to act to a certain extent as his amanuensis 

 and aid in putting the results of his experiments in the 

 form of reports to the Light House Board. In this way 

 I became interested in this work and was, in a very 

 humble way, associated with Professor Henry in its pros- 

 ecution. Thus I entered with him into a practical dis- 

 cussion of the subject and became, after a fashion, pos- 

 sessed of his views as to the best way to follow up the 

 investigation. I thus came to know something of his 

 tentative plans and of his desire to make very practical 

 use for light house purposes of the outcome of the in- 

 vestigations. 



On Nov. 6, 1880, the great Long Island Sound steamer 

 Rhode Island was stranded and finally lost on Bonnet 

 Point in Narragansett Bay. Then, putting it roughly, a 

 million in property was lost and thousands of lives were 

 imperilled. The master and pilot of the steamer claimed 

 that the fog-signal at Beaver Tail Point, about one and 

 seven-eighths miles away, was not sounding at the time 

 of the accident; and hence the casualty. The light 

 keeper who was in charge of the fog-signal at the time, 

 and who was in peril of losing his place, proved con- 

 clusively that at the time of the wreck the sound of the 

 fog-signal was heard at Newport, five miles away, at Fort 

 Adams, four and a quarter miles away in one direction, 

 and at Narragansett Pier, four and a half miles away in 

 another direction. The steamer people, who were in 

 danger of forfeiting their licenses, came back with affi- 

 davits of many on board that they were anxiously listen- 

 ing for the fog-signal, and that it was not in operation, 

 for they did not hear its sound. 



Then the Light House Board took a hand in the mat- 

 ter. It had been shown by Professor Henry that, although 

 a sound could be heard at a certain distance from its 



'Read before the Philosophical Society of Washington, Nov. 25, 1893. 



source, it might not be heard in the same direction, and 

 at the same time, at a less distance. Could this be one 

 of those cases ? A naval officer in the service of the 

 board, now ranking as a Commodore, was sent to the 

 locality to find out. He had the fog-signal at Beaver 

 Tail started, and cruised round it in a sail boat for some 

 time, taking constant note of the intervals of the sound. 

 He found, and reported to everybody's surjsrise, that not 

 only did he fail to get the sound of the Beaver Tail fog- 

 signal at Bonnet Point, one and seven-eighths miles away, 

 where the Rhode Island was lost, but he failed to get it 

 at other points even nearer to the fog-signal, while he 

 heard it on the same day at different points farther away, 

 and much farther away in a line with the nearer points 

 where he could not hear it. This settled the question. 

 The light keeper was relieved from the charge of failing 

 to have the fog-signal in operation, and the steamer 

 people were relieved from the charge of failing to act on 

 the warning of the fog-signal, which was blowing, but 

 which, while within earshot, they might not hear. 



In 1881 the great propeller Galatea, while on the way 

 from New York to Providence, ran onto Little Gull Island 

 in Long Island Sound, imperilling many lives and much 

 property. There was, and is, on that island, which is but 

 one-eighth of amile long, apowerful light and a powerful 

 fog-signal. That fog signal has been often heard sixteen 

 miles away. The defense of the steamer people was that 

 the fog was dense and that the fog-signal was not blow- 

 ing. The light-keeper, in his defense, showed that the 

 fog-signal was blowing, that it was heard and noted at 

 several different points in different directions, say at New 

 London, Mystic, and at several light houses, many miles 

 away, at the very time the Galatea ran on the little islet 

 on which the fog-signal was at work. Again the Light 

 House Board was required to look into the matter. 

 Again careful investigation was made. And again it was 

 shown that the fog-signal might be heard far off, 

 and not close to, and the spots where it was not heard 

 were noted and plotted on the chart; and again the 

 steamer people and the light house people were exoner- 

 ated from blame. 



In 1881 I gathered these facts and submitted them to 

 the Philosophical Society. My paper was printed in the 

 Bulletin of the Society, and it was largely copied in mari- 

 time and scientific publications in this and other coun- 

 tries. The light house establishments of England, France 

 and Spain reprinted the paper, each in its own language. 

 And the eminent Emile AUard, head of the French light 

 house establishment and a prominent officer of the French 

 Corps of Engineers, plotted my numerical statement of 

 the intensity of sound as heard from the fog-signals, in 

 ;^'raphic form, that is, in lines of various width, and sent 

 his diagrams to me in a letter in which he discussed the 

 subject at length. 



The Light House Board meantime was considering the 

 matter from a purely practical standpoint. If, it was 

 reasoned, there is a point within earshot of a fog-signal, 

 where, from any cause, the fog-signal cannot be heard, 

 then some other signal should be placed at that point, 

 from which vessels can take a fresh departure. Acting 

 upon that idea, investigation was made as to the region 

 about each prominent fog-signal which it had been said 

 could not be heard at points where it ought to be heard. 

 In several instances I was sent to such points to make in- 

 vestigation and to report with recommendations. In the 

 summer of 1885 I cruised about Point Judith, R. I., and 

 the southeast end of Block Island, both at the entrance 

 of Long Island Sound, and about the light house and fog- 

 signal on Little Brewster Island, entrance to Boston 

 Harbor. An area of silence was found and plotted about 

 one and a quarter miles south of Point Judith, where the 



