1875] 



WRITINGS OP JOSEPH HENRY. 



473 



origin of sound however must not be too great relatively to 

 the elevation of the observer; otherwise it will pass over his 

 head, as well as over that of the observer at the surface of the 

 earth. In most instances the sound was not continuous, but 

 was interrupted, — heard for a time, then lost; again becom- 

 ing audible, it was heard until finally lost. Besides this, it 

 was difficult to determine when the sound ceased to be 

 heard, since this depended on the sensibility of the ear and 

 the greater or less attention of the observer at the time of the 

 observation. To obviate these difficulties, as well as the 

 unfavorable condition of too great a distance of the origin of 

 sound from the observer, it was concluded to adopt as the 

 duration of the sound the elapsed time between its begin- 

 ning and the period when it was first lost. 



The observer on the tower was Mr. P. Barnard, while the 

 one below was General Woodruff. From the records of the 

 observations of these gentlemen the following tables are 

 compiled, the first of which indicates the relative duration 

 of sound on the top of the tower and at the bottom, — the 

 sound moving against the wind; the second the same dura- 

 tion, the sound moving with the wind; and the third, the 

 same with the sound at right angles to it. 



Table 1. — Sound against the wind. 



