TRANSMISSION OF SOUND-SIGNALS DURING FOGS AT SEA. 1'J5 



The suggestions of scientific men to the Commissioners of Light-houses 

 refer principally to sounds propagated in air. Dr. Robinson points out that 

 the sound should be as discordant as possible with that of the wind and 

 waves, which are said to belong to C. He thinks that sound should be pro- 

 duced as near the sea-level as possible. Mr. Mallet calls attention to explo- 

 sive sounds as assisting the ear in ascertaining direction. Admiral FitzRoy 

 suggests sharp high-pitched notes, with trumpet-mouthed devices for ascertain- 

 ing the direction. He thinks that the source of sound should be at a low 

 level. Sir John Herschel recommends the trial of a battery of steam-whistles 

 blown by high-pressure steam ; by a combination of three or several sets of 

 three whistles pitched exactly to harmonic intervals (key note third, fifth, and 

 octave), and with a rattle which intensifies the action on the auditory nerve. 

 He also suggests concave reflectors, and the subaqueous propagation of sound 

 by explosions in the foci of large and heavy parabolic reflectors. Professor 

 Potter suggests the use of ear-trumpets, in order to assist observers. Pro- 

 fessor Rankine recommends a parabolic ear-trumpet for the determination of 

 direction. The Abbe Moigno maintains that a continuous grave sound spreads 

 further than a very acute violent sound. Thus he instances the greater 

 distance at which the sound of a cannon can be heard compared to thunder. 

 He suggests resonant tubes like those attached to Savart's acoustical ap- 

 paratus. He thinks such resonant tubes far more effective than reflectors. 

 He also recommends, for ascertaining direction, the use of a dififerential ear- 

 trumpet, like Dr. Scott Alison's stethophone*. He thinks that sound should 

 be produced close to, or even in the water, and that a series of defined sounds 

 could be arranged beforehand, one being assigned to each maritime station. 

 He refers to M. Colladon's experiments for details relative to subaqueous 

 sounds. Mr. J. Mackintosh, of Liverpool, makes a suggestion in complete 

 accordance with M. Colladon's (inclusions. He suggests a deep well in 

 light-ships, whence the sound of a large bell might be propagated all around 

 through the water. A kind of hydrophone applied from a vessel to the 

 water might enable an observer to find the position of the light-ship. These 

 suggestions contain nearly all the information presented in the Report on 

 Light-houses and Beacons. Remarks made by other gentlemen are either 

 equivalent to some of the foregoing, or have reference only to some improve- 

 ments in the details of the existing system of fog-bells. 



Professor Wheatstone has informed me that it had been his intention, in 

 co-operation with the late Mr. Robert Stephenson, to institute a series of ex- 

 periments on sound, with reference to fog-signals. For this purpose Mr. 

 Stephenson intended to employ his own yacht ; and had he been spared longer 

 to science, the information we possess would probably have been less meagre 

 than it is. Professor Wheatstone thinks that a battery of shrill whistles 

 very nearly, but not entirely in unison would be most effective in forcing 

 sound through a fog. Liquid and solid conductors should be as much as 

 possible availed of during fogs. Water would be a far better conducting^ 

 medium than air for assisting in the determination of direction. 



If we are entitled to come to any positive decision upon the evidence which 

 we possess, I should say that water seems to present in a higher degree 

 than air during fogs, the qualities required in a sound conductor. High- 

 pitched sounds seem to be generally acknowledged as most penetrating 

 during fogs, but we have little information as to the detection of the direction 

 of such sounds. On the other hand, we already possess a clue to the direc- 

 tion of subaqueous sounds in M. Colladon's acoustic shadow. Upon the 



* Proceedings of the Royal Society, and Phil. Mag. May 1858. 



