468 



WRITINGS OF JOSEPH HENRY. 



[1875 



the results obtained on August 10, in Fig. 5, converting the 

 distances into miles, referring them to a common centre, and 

 tracing through the several extremities of the lines repre- 

 senting the distances — a continuous line, which may be desig- 

 nated as the curve of audibility. C being the centre to which 

 the sounds are referred, C A represents the distance at which 

 the sound was heard against the wind, and B, in the direc- 

 tion of the wind, while G E and G D represent the distance 

 at right angles to the wind, and C i^and G G the distances 

 respectively with and against the wind on an intermediate 

 course. 



Fig. 5. 



The curve which is presented in the foregoing figure may 

 be considered as that which represents the normal limit of 

 audibility during the two days in which the experiments 

 were made. The line D E divides the plane of the curve 

 into two unequal portions, D A F E and D G B E, the 

 former representing the audibility of sound moving against 

 the wind, and the other the audibility of sound moving with 

 the wind. 



We can scarcely think that any other condition of the air 

 than that of its motion could produce a result of this kind. 

 It exhibits clearly the fact that sound is not heard as a gen- 

 eral rule at ris^ht ang;les to the wind farther than with the 



