526 



RESEARCHES IN SOUND. 



Tlie following table exMbits at one view tlie results of the foregoing 

 experiments, wJiich relate to sound moving against tlie wind, and with, 

 the ^yind, reduced to miles. 



These results are in accordance with those of all the direct observa- 

 tions which had previously been made on sound in regard to wind by 

 the Light-House Board, with the exception of those at Sandy Hook in 

 September, 1874, as given in the last report, in which the sound was 

 heard from a steamer farther against the wind than in the direction of 

 the wind. This anomaly was explained by the existence of an upper 

 current of air, moving in an opposite direction to that at the surface^n 

 accordance with the hyiwthesis of the refraction of sound. 



It. will be observed that four of the experiments give exactly the same 

 distances to represent the audibility of sound with and against the 

 wind. This coincidence was not observed untU after the notes were 

 collated for discussion, and, if not accidental, was due to the equal ve- 

 locity of the wind and the general conditions of the atmosphere on the 

 two days. 



To give a definite idea of these relations we have plotted the results 

 obtained on August 10, in Fig. 5, converting the distances into miles and 

 refeiTing them to a common center, and tracing through the several ex- 

 tremities of the lines representing the distances a continuous line, which 

 may be designated as the curve of audibility. C being the center to 

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

 sound was heard against the wind, and CB in tlie direction of the wind, 

 while C E and D represent the distance at right angles to the wind^ 

 and I" G and G the distances resijectively with and against the wind 

 on an intermediate course. 



