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WKITINGS OP JOSEPH HENRY. 



[1875 



Figure 3 represents the disturbing effect of two winds, the 

 lower in opposition to the sound, and the upper with it. 



FlQ. 3. — Compound wind. 



In this case the principal effect will be a depression of the 

 sound-beam, similar to that shown in Figure 1, but more 

 strongly marked, as the difference of motion will be greater 

 as we ascend. Attending this action, says Mr. Taylor, there 

 will probably be some lagging of the lower stratum by reason 

 of the surface-friction, the tendency of which will be to dis- 

 tort the lower part of the sound-waves, giving the lowest 

 sound-beam a reverse or serpentine curvature. Such an 

 effect is represented by the lower line s t o, (Figure 3,) the 

 lower ray being at first turned up (by the adverse wind, 

 somewhat as shown in Figure 2) and afterward thrown down 

 by the dominant influence of the higher current of air, ren- 

 dering the sound less audible at an intermediate point — t, 

 than at the more distant station o. This hypothetical case of 

 compound refraction offers a plausible explanation of the 

 paradox of a nearer sound being diminished in power by 

 the wind which increases the effect of a more distant one. 



In these figures and all the succeeding ones, the direction 

 of the wind is indicated by arrows. 



The hypothesis we have adopted (in connection with the 

 fact of the lateral spread of sound) gives a simple explanation 

 of various abnormal phenomena of sound such as have been 

 observed in the previous investigations, and of which the 

 following are examples: First, the audibility of a sound at a 

 distance, and its inaudibility nearer the source of sound; 

 second, the inaudibility of a sound at a given distance in 

 one direction, while a lesser sound is heard at the same dis- 

 tance in an opposite direction; third, the audibility of the 

 sound of an instrument at one time at the distance of several 



