EESEARCHES IN SOUND. 



523 



conformity with the theoiy of the refraction of sound which we have pre- 

 viously exphiiued. 



The following recapitulation of the results of the foregoing experi- 

 ments will exhibit their correspondence with the general theory : 



Sound lieard coming against the wind. 



Experiments. 



First - . . 

 Third . . 

 Fifth... 

 Seventh 

 Eighth . 



Average . 



Duration at the 

 top of the tower. 



4^ minutes 



12 minutes 



12 minutes 



d minutes 



6 minutes 



42^ minutes 

 8^ minutes 



Duration at the base of 

 the cliff. 



■i minute 



5^ minutes 



5^ minutes 



Not heard 



First blast heard, but 

 no other, 

 i minute after starting. 



12 minutes. 



2.4 minutes 



Difference in favor of 

 audition on the tower. 



4 minutes. 



6^ minutes, 



6| minutes. 



8 miuuies. 



5i- minutes. 



30^ minutes. 

 6. 1 minutes. 



Sound lieard coining xcith the wind. 



From the first of the foregoing tables it appears that the elevation of 

 the observer has a marked effect on the audition of sound moving against 

 the wind while, from the second, with one important exception, it has 

 very little, if any, effect on sound moving with the wind. Another ex- 

 periment relative to the same class of phenomena was made on the 19th 

 of August (see Fig. 4), the wind being S. S. W. Two observers, General 

 Woodruff and Dr. Welling, starting from the bottom of the cliff" imme- 

 diately below the light-house, went along the beach, the one in the direc- 

 tion A /, and the other in direction A e. General Woodruff found that 

 the sound of the siren was distinctly heard all the way to the break- 

 water, and was so loud that it probably could have been heard for sev- 

 eral miles in that direction. Dr. Welling, on the contrary, entirely lost 

 the sound within a quarter of a mile of the light-house. This result is 

 readily explained as a case of lateral refraction; the wind was in the 

 direction traversed by General Woodruff, and contrary to that pursued 

 by Dr. Welling. In the one case the wind, retarded by the surface of 



