476 WRITINGS OF JOSEPH HENRY, [1875 



angles of azimuth and time of sailing. The steamer was 

 directed to proceed, as indicated in Fig. 7, 1st, against the 

 wind, so that the sound would come to the observers with 

 the wind; 2d, at right angles to the wind ; 3d, in an inter- 

 mediate direction between the last course and the direction 

 of the wind ; 4th, approximately with the wind, so that the 

 sound would come to the ears of the observers against the 

 wind ; 5th, in an intermediate direction ; and, 6th, again at 

 right angles to the wind. It was supposed that by this ar- 

 rangement a symmetrical curve of sound would be obtained ; 

 and we think this would have been the case had the wind 

 remained constant in direction. It did remain nearly the 

 same during the time of describing the first, second, and third 

 courses, and only slightly varied during the fourth ; but pre- 

 vious to running the fifth and sixth courses the wind had 

 changed to a direction nearly at right angles to its first course. 



As is shown in Fig. 7, the first, second, third, and fourth 

 courses form a normal curve of audition ; the fifth and sixth 

 courses however give discordant results, being much longer 

 than a symmetrical curve would indicate, showing a change 

 in the condition of the medium from that which existed 

 during the running of the other courses ; this change was 

 evidently that of the wind, which veering (as above stated) 

 through an arc of a little more than 90°, brought it nearly 

 at right angles to the fifth course, and approximately in the 

 direction of the sixth course; the wind also increased its 

 velocity. These changes are sufiicient, without other consid- 

 erations, to give a rational account of the phenomena ob- 

 served. They both tend to increase the distance at which 

 the sound would be heard. 



In these experiments, as in subsequent ones, it is to be re- 

 gretted that for want of balloons the motion of the air above 

 could not be ascertained, as was done at Sandy Hook in Sep- 

 tember, 1874. Previous to sailing from the depot at Staten 

 Island attempts had been made to secure a supply of toy 

 balloons, but none could be found at that time in the city of 

 New York. Arrangements were therefore made for procur- 

 ing a reservoir of condensed hydrogen, by which India-rub- 



