1875] WRITINGS OF JOSEPH HENRY. 465 



the same pressure of 20 pounds of steam, and which by pre- 

 vious comparison — had been found to give sound at this 

 pressure of the same penetrating power. The observations 

 on the Mistletoe were made by General Woodruff, and on the 

 Putnam by Dr. Welling, each assisted by the officers of the 

 respective vessels. The two steamers proceeded to the buoy, 

 — off the north end of the isl|Lnd, in which position the wind 

 was unobstructed by the land — a low beach. Indeed, the 

 Island being entirely destitute of trees, and consisting of a 

 rolling surface, the wind had full sweep over it in every 

 direction. 



First experiment. — The Putnam went against the wind and 

 the Mistletoe in the opposite direction. The Putnam lost the 

 sound of the whistle of the Mistletoe in two minutes and 

 stopped, but continued to blow the whistle. The Mistletoe 

 ■continued on her course and heard the Putnam's whistle for 

 twenty minutes in all. During the first two minutes both 

 vessels were in motion, and therefore the space through 

 which the sound was heard moving against the wind — would 

 be represented by 4, while the space tlirough which the 

 .sound was heard moving with the wind — would be repre- 

 sented by 20 + 2 = (22), the ratio being 1:5J. 



Second experiment. — In this, the Putnam went with the 

 wind and the Mistletoe in the opposite direction. The Mis- 

 tletoe lost the sound of the Putnam's whistle in two minutes. 

 The Putnam then stopped and remained at rest, while the 

 Mistletoe continued on her course until the Putnam lost 

 sound of her whistle, twenty-six minutes later. As both 

 steamers were separating during the first two minutes with 

 equal speed, the distance travelled by the sound heard mov- 

 ing against the wind is represented by 4, while the distance 

 of the sound heard with the wind is represented by 26+2= 

 28, the ratio being 1:7. It should be mentioned however 

 that the notes in this experiment are defective and some- 

 what discrepant. 



Tliird experiment. — The Putnam went against the wind, 

 ihe Mistletoe in the opposite direction. The Putnam lost 

 -the sound of the whistle of the Mistletoe in two minutes, 

 30 



