44 BULLETIN OF THE 



not regained until the vessel approached within a quarter of a mile 

 of the station. During all this time of silence the sound of the 

 steamer's whistle was distinctly heard at the Whitehead station ; 

 that is, a lesser sound was heard from the steamer to the station, 

 " while a sound of greater volume was unheard in 'the opposite di- 

 rection." The wind at the time was blowing in favor of the 

 steamer's whistle, and against the fog-signal.* 



In a paper presented to the Royal Society in 1874, Prof. Rey- 

 nolds showed that the form of the sound-wave is liable to flexure 

 from changes in the temperature of the atmosphere as well as from 

 the unequal motion of wind.f 



These abnormal phenomena of sound, considered in connection 

 with the hypothesis of Prof. Stokes, as enlarged and applied by 

 Prof. Henry, may be reduced into the following generalizations 

 which, if accurate in point of logical form, and true in point of the 

 facts to which they are applied, may be stated under the guise of 

 aphorisms, as follows : 



1. "Where the condition of the air is nearest that of a calm, 

 the larger will be the curve of audition, and the nearer will the 

 shape of the curve approach to a circle, of which the point of 

 origin of the sound, or the point of perception will be the centre." 

 [This aphorism is stated abstractly from any consideration of tem- 

 perature refraction which, so far as it exists, will always tend to 

 modify the shape of the curve of audition. ]| 



2. Apart from all consideration of temperature refraction, a 

 sound will be heai'd furthest in the direction of a gentle wind, be- 

 cause the portion of the sound-wave thrown down from above, in 

 this case, is re-enforced by the sound reflected from the surface, 

 and will thus more than compensate for the loss by friction. || 



3. Other things being equal, the area of audition will be propor- 

 tionally diminished in the case of sounds moving against winds 

 more or less strong, because the sonorous waves will be refracted 

 above the ears of the observer. (Stokes, Henry and Reynolds.) 



*Rep. Light-House Board, 1874, p. 108. 



f London, Ed., and Dublin Phil. Mag. for 1875, Vol. 50, p. 52. 

 % Light-House Report for 1875, p. 125. 



\ Ibidem. Cf., Tyndall's Sound, p. 311. Cf., Reynolds in Lon., Ed., and 

 Dub. Ph. Mag. for 1875, Vol. 50, pp. 63, 68. 



