484 WRITINGS OF JOSEPH HENRY. [1875 



was that of the greater velocity of the wind, both at the sur- 

 face of the sea and at the top of the tower, and by compar- 

 ing the several figures in regard to the wind it will be seen 

 that where the condition of the air was nearest that of a 

 calm the larger was the curve of audition, and the nearer 

 the figures approach to a circle, of which the point of origin 

 of sound (or the point of perception) is the centre. From 

 these facts we are inclined to think that sound is not heard 

 as far during a time of high wind in any direction as it is 

 during a perfect calm, and that it is heard farthest with a 

 gentle wind. This conclusion, which was not anticipated at 

 the beginning of these investigations, is we think in strict 

 conformity with the hypothesis adopted. In the case of sound 

 moving against a strong wind, the sonorous waves being 

 thrown up above the ears of the observer, the sphere of audi- 

 tion in that direction is without question greatly diminished; 

 and that it should also be diminished when sound is moving 

 with a strong wind having a greater velocity above than below 

 is not difficult to conceive. In this case the sound-wave will 

 be so thrown down against the earth, and so much of it 

 absorbed, as to weaken the intensity of that part which reaches 

 the ear, while in the case of a feeble wind moving faster 

 above than below, the portion of the wave thrown down 

 from above will only be sufficient to compensate for the 

 smaller loss by friction, and thus the sound may be heard 

 at a greater distance than in still air. But on this point, as 

 well on as others, further experiments are required. 



While we consider the wind as the principal agent in pro- 

 ducing the abnormal phenomena of sound, we do not by any 

 means regard it as the sole agent. Prof. Osborne Reynolds, of 

 Owens College, Manchester, England, without any knowledge 

 of investigations in America on this subject, instituted a 

 series of experiments on the effect of wind upon sound, and 

 finally adopted precisely the same hypothesis which we have 

 used for generalizing the observed phenomena. He has 

 however, in a very ingenious and important paper presented 

 to the Royal Society in 1874, extended the same principle 

 to the effect of heat in changing the form of the sound-wave, 

 and has shown — both by reasoning and experiment, that the 



