RESEARCHES IN SOUND. 

 Fig. 5. 



527 



The curve which is presented in the foregoing figin^e may be considered 

 as that which represents the normal hmit 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 mo\ing 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 general rule at right angles to the wind 

 farther than with the wind, as has been asserted. In this case the ratio 

 of the latter to the former is as 11 to 6, or nearly double. 



The investigation of the relation of wind to the penetration of sound 

 was renewed in a series of subsequent exj^erimeuts, the results of which 

 are to be given in a succeeding part of this report. 



It should be observed, in comjiaring Fig. 5 with the subsequent fig- 

 ures representing the curve of audibility, that the arrow representing 

 th& direction of the wind points in the longest direction to the figure, 

 whereas in other figures the j)ointing is in the oiiposite direction. The 

 difference arises from the fact that in Fig. 5 the sound is supposed to 

 radiate from the center, C, while in the others the sound converges to. the 

 center as a point of observation. The foregoing diagram and all that 

 follow in this report were^ plotted by Mr. Edward Woodruff, assistant 

 superintendent of construction of the third light-house distiict. 



