534 RESEARCHES IN SOUND. 



supposed that by this arrangement a symmetrical curve of sound would 

 "be obtained ; and we tliink tbis 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 i)revious 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 we have seen, through 

 an arc of a little more than OO©, 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 sufficient, without 

 other considerations, 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 ex])eriments, as in subsequent ones, it is to be regretted that 

 for want of balloons the motion of the air above could not be ascer. 

 tained, as was done at Sandy Hook in Seiitember, 1874. Previous to 

 sailing from the depot at Staten Island attemjjts had been made to se- 

 cure 11 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-rubber balloons 

 could be inflated at the time they were wanted. Unfortunately this ap- 

 l^aratus did not arrive in time to be of much avail in this series of experi. 

 ments. Besides this, on account of the smalluess of the balloons, the 

 ascent was too slow compared to the horizontal motion to indicate the 

 direction of the wind at a considerable elevation above the points of 

 observation. They were however of use in jiointing out definitely the 

 direction of the wind and the changes it was undergoing. Moreover, at 

 the time of leaving New York we were only able to procure one ane- 

 mometer, whereas we ought to have had a number, one for the top of 

 the tower, one for the bottom, and one for each vessel. 



Experiments of September 3. — Barometer, 30.02 inches ; thermometer, 

 dry bulb, 72^.5 F. wet bulb, 70° ; wind from the east, but too slight to 

 move the cups of the anemometer ; it soon however spang up from the 

 opposite direction, in which it continued during the remainder of the 

 day, attaining a velocity of five and a quarter miles per hour. 



In these experiments two light-house steamers were employed, the 

 Mistletoe and Cactus, which enabled us to obtain the results in half the 

 time, and thus to obviate the effect, in some degree, of any change in 

 the direction of the wind. On this occasion the sound was noted at the 

 light-house as it converged to a center from the whistle of each vessel, 



