58 TRANSACTIONS. I9OI-2 



coming this difficulty. American inventors have taken 

 advantage of this direction of the sound to equip a siren with 

 megaphones directed to tlie cardinal points. Through each 

 magaphone it sends a different signal, with the expectation 

 that a vessel can judge the direction from which the sound 

 comes by the relative loudness of the signals. We are now 

 installing one of these Hamilton-Foster" sirens at Fame 

 point lighthouse, on the Gaspe coast, the first landfall made 

 by vessels after crossing the Gulf inward bound, to experi- 

 ment on this principle of judging sound direction. Even 

 though the claim of the inventors, that the siren will indicate 

 its own direction from the vessel, should be unfulfilled, the 

 siginal will give an efficient coast warning, acting as an ordi- 

 nasy siren. 



We meet with a good deal of difficulty and disappoint- 

 ment in operating our fog signals. This is because we cannot 

 make mariners understand that sound signals are extremely 

 liable to aerial disturbance. The'retically^ sound waves are 

 propagated in straight lines in all directions from their source, 

 exactly as light waves are propagated. Practically^ these 

 straight lines of sound waves are deflected by any little 

 irregularity in the air through which they pass. If the air is 

 not wholly homogeneous, the sound waves will not pass, 

 through it in straight lines, but will be deflected, and whether 

 the deflection is down towards the surface of the water, or up 

 into the air, the effect is the same; the sound does not travel 

 parallel to the surface of the- sea, and is lost to the sailor who 

 is listening for it. A small island, a reef, or rocks, or even a 

 shoal lying outside of a fog alarm station, will have the eflfect 

 of unequally heating the air which covers them, and the air 

 thus separated into strata of unequal densities, causes refrac- 

 tion of the waves of sound, and the fog alarm becomes in- 

 effective. The same thing may happen, though it is not so 

 likely to do so, where none of these natural obstructions are 

 apparent. Times without number complaint has been made 

 that one of our fog alarms was not in operation, when inves- 



