PHILOSOPHICAL SOCIETY OF WASHINGTON. 23 



Mr. A. B. Johnson presented the following communication on 



RECENT INVESTIGATIONS BY THE LIGHT-HOUSE BOARD ON THE 

 ANOMALIES OF SOUND FROM FOG SIGNALS. 



Among our erroneous popular notions is one which occasionally 

 brings practical men, even ship-masters, to grief. It is the idea 

 that sound is always heard in all directions from its source accord- 

 ing to its intensity or force, and according to the distance of the 

 hearer from it. Instances of this fallacy have accumulated, and 

 they are emphasized by shipwrecks caused by the insistance of 

 mariners on the infallibility of their ears, who have accepted un- 

 questioned the guidance of sound signals during fog as they have 

 that of light-houses during clear weather. The fact is, audition is 

 subject to aberrations, and under circumstances where little ex- 

 pected. We have learned by sad experience that implicit reliance 

 on sound signals may, as it has, lead to danger if not to death. 



The wreck of the steamer Rhode Island, on Bonnet Point in 

 Narragansett Bay, which happened on November 6, 1880, when a 

 million dollars in property was lost, was caused, it was said, by the 

 failure of the fog-signal on Beaver Tail Point to sound at that 

 time. Thereupon the Light-House Board, which has charge of the 

 sixty and more fog-signals on our coasts, made an investigation 

 which showed that the fog-signal was in full operation when the 

 wreck took place ; but it also brought out the fact, that while there 

 was no lack in the volume of the sound emitted by the signal, there 

 was often a decided lack in the audition of that sound, so much so 

 that it would not be heard at the intensity expected, nor at the 

 place expected ; indeed it would be heard faintly where it ought to 

 be heard loudly, and loudly where it ought to be heard faintly ; that 

 it could not be heard at all at some points, and then further away 

 it could be heard better than near by ; that it could be heard and 

 lost and heard and lost again, all within reasonable ear shot, and 

 all this while the signal was in full blast and sounding continu- 

 ously. 



The following table, A, will give the results obtained by the of- 

 ficer of the navy who investigated these phenomena, and reported 

 to the Light-House Board : 



