1874] WRITINGS OF JOSEPH HENRY. 441 



opposing wind observed were confined to the region near 

 the surface. An unsuccessful attempt to test this hypothesis, 

 was made by means of a balloon of tissue-paper, constructed 

 by Major Hains, but which was unfortunately burned in the 

 attempt to inflate it with heated air. 



The remainder of this day was devoted to observations on 

 the sound of the siren at the light-house at Sandy Hook. 

 For this purpose the Cactus, under Captain Davis, was 

 directed to steam in the eye of the wind, while the 31istletoe, 

 under General Woodruff, steamed before the wind, and the 

 Putnam steamed at right angles to the wind. Unfortu- 

 nately, on account of the diminution of light at the closing 

 in of the day, nothing could be observed. The only result 

 obtained was that one of the duplicate sirens was heard 

 more distinctly than the other, namely the one with the 

 higher note. 



Experiments September 24, 1874. — The place chosen for 

 the observations of this day was still farther out on the 

 ocean, at the Sandy Hook light-vessel, 6 miles from the 

 nearest point of land. The pressure of the atmosphere was 

 a little greater than the day before, being 30"52; the tem- 

 perature about the same, 72° Fahr., wind light, from a 

 westerly direction, as on the previous day, with a force (as 

 indicated by the anemometer,) of 1'2 miles per hour. Hav- 

 ing been provided with a number of India-rubber toy bal- 

 loons, the two vessels were sent off in opposite directions, — 

 leaving at 10:40 a. m., the Mistletoe toward the west, against 

 the wind, the Cactus toward the east, with the wind. A 

 change was also made in observing the sound. In these ob- 

 servations the sound was noted at each vessel from the other, 

 the speed of the steamers being the same ; the distance be- 

 tween them when the Mistletoe lost the sound of the Cactus 

 was two miles, while the Cactus continued to hear the Mistle- 

 toe's sound (coming with the wind) until they were four miles 

 apart. Simultaneously with this observation a balloon was 

 let off from the Putnam at the light-vessel, which in its 

 ascent moved continuously obliquely upward in a line 

 slightly curving toward the horizon, in the direction of the 



