1875] 



WRITINGS OF JOSEPH HENRY. 



:<0 



the wind. Were it not for the result of the first experiment 

 of this class at Block Island, we should not hesitate to adopt 

 this as a general conclusion. 



From the general mean of observations given in Table 3, 

 it would appear that the sound moving at right angles to 

 the wind can be heard better at an elevation than at the 

 surface, — a result not anticipated. 



Observations on Effect of Wind on Sound. — This series was 

 commenced on the 2d of September. Barometer, 30"3 inches ; 

 thermometer, dry bulb, 70-5° F., wet bulb, 67-5°; wind at the 

 surface of sea six miles per hour, and variable : at 3 p. m. the 

 velocity was eight miles at the surface. (See Fig. 7.) 



«^ 



Fia. 7. 



The experiments were made by means of the steiimer 

 Mistletoe, which proceeded from the light-house, as a centre, 

 in different directions, blowing the whistle every half-minute, 

 and returning at a signal, when the sound was lost ; the 

 time being noted by different observers, and the distance 

 estimated by the position of the steamer in reference to 

 known objects on the Coast Survey chart, as well as by 



