1875] 



WRITINGS OF JOSEPH HENRY, 



449 



ence, by Mr. William B. Taylor, on "Recent Researches in 

 Sound," as the present report is passing through the press. 



— . N *. >. ^^JL- — 1 -I r 



FiQ. 1. — Favoring wind. 



In these cuts, Figure 1 represents the effect of a favorable 

 wind in depressing the waves of sound ; s being the signal- 

 station and the point of observation. The wind blowing 

 from TFto E, as the spheroidal faces of the sonorous waves 

 become more pressed forward by the greater velocity of the 

 wind above, (assuming it to be retarded at the surface by 

 friction,) and the direction of the acoustic beam being con- 

 stantly normal to the wave-surfaces, the lines of direction 

 of the sound will gradually be bent downward and reach 

 the ear of the observer with an accumulated effect at the 

 point o; being re-enforced by the lower sound-rays which 

 are reflected from the surface of the water. 



-n'n \ '\ \ \ \ \ \ \ \ \ \ \ \ \ \ 



Fig. 2. — Adverse wind. 



Figure 2 represents the ordinary effect of an opposing 

 wind here blowing from E to W against the sound ; the 

 wave-faces being more resisted above than below by the 

 swifter wind, (assuming as before a retardation at the sur- 

 face,) the sound-beams are curved upward, and the lowest 

 ray that in still air would reach the distant observer at o, 

 is gradually so tilted up, that it passes above the ear of the 

 listener, leaving him practically in an acoustic shadow; 

 even after due allowance made for the divergence of the 

 sound by dissipation downward. 

 29 



