350 MEMORIAL OF JOSEPH HENRY. 



others were directed in opposite courses, one with the wind, or east- 

 ward, the other against it, or westward. In 15 minutes the whistle 

 of the former ceased to be heard, while that of the latter was very 

 distinctly heard; the anemometer showing a wind of about six 

 miles per hour. About noon the vessels changed positions, but the 

 sound from the w r est continued audible for about three times the 

 distance of that from the east, though the wind had declined to 

 nearly a calm or to about half a mile per hour. In an hour and a 

 half the wind had changed to "within two points of an exactly 

 opposite direction, blowing from the indications of the anemometer 

 at the rate of ten and a half miles per hour/' The vessels once 

 more departing, one with the wind, the other against it, the sound 

 of the whistle coming against the wind was this time heard for the 

 greater distance, contrary to expectation. On the following day a 

 number of small balloons having been provided, a similar series of 

 experiments to that of the preceding day was made ; a station being 

 selected at a greater distance from land. On the first trial, with a 

 light wind from the west of about one and a quarter miles per hour 

 as indicated by the anemometer, a balloon was set off which con- 

 tinued rising and moving eastward till lost to sight. Two of the 

 vessels taking opposite courses as before, gave the sound in the 

 direction of the wind about double the duration of that coming 

 against the slight wind. The vessels then changed places in their 

 opposite courses; the wind having subsided to a calm. "A balloon 

 let off ascended vertically until it attained an elevation of about 

 1,000 feet, when turning east it followed the direction of the pre- 

 vious one. In this case the sound of the whistle coming from the 

 east was heard somewhat longer than the opposite one. At the 

 third trial made after noon, the wind had changed nearly one-third 

 of the circle, its force being about five miles per hour. The vessels 

 once more taking their courses with the wind and against it, " several 

 balloons set off at this time were carried by the surface wind west- 

 wardly until nearly lost to sight, when they were observed to turn 

 east, following the direction of the wind traced in the earlier obser- 

 vations." In this case the sound was heard with the wind very 

 slightly farther than against it. It was thus shown that the upper 

 current of wind had remained constant throughout the day, while 



