KESEARCHES IN SOUND. 559 



of a distinct echo, apparently from a spa^e near tbe horizon of fifteen or 

 twenty degrees in azinuith, directly in the prolongation of the axis of 

 the trnmpet. The londness of this echo depends upon the loudness and 

 quantity of the original sound, and therefore it is produced with the 

 greatest distinctness by the siren. It cannot be due to the accidental 

 l^osition of a flocculent portion of atmosphere, nor to the direct reflection 

 from the crests of the waves, as was at first supposed, since it is always 

 he^ird except when the wind is blowing a hurricane. 



As a provisional explanation, the hyjiothesis has been adopted thst 

 in the natural spread of the waves of sound, some of the rays must take 

 such a curvilinear course as to strike the surface of the water in an 

 opi)osite direction and thus be reflected back to the station or location 

 of the origin of the sound. 



Light-House Board, October^ 1877. 



