434 WRITINGS OF JOSEPH HENRY. [1874 



the sound was with the wind. The result of these obser- 

 vations was conformable to that generally obtained from 

 previous ones, namely that the sound is seldom or never 

 heard at the same distance in different directions, and more- 

 over that it is generally heard farther with the wind than 

 against it. 



The observations of this day also illustrate the spread of the 

 sound-wave on either side of the axis of the trumpet, a fact 

 which has frequently been noticed in other investigations. 

 It may be well to mention that the siren trumpet at this 

 locality is directed horizontally, with its prolonged axis pass- 

 ing over a space of very rough ground, (immediately in front 

 of the mouth of the trumpet,) the surface of which is prin- 

 cipally composed of bowlders : one of these (of very large 

 size) is directly in front of the trumpet, and the idea occurred 

 to me that this rough surface might produce some effect on 

 the transmission of sound to a distance. I observed b}'- 

 strewing sand upon a paper that the former was violently 

 agitated when held near the surface of the large bowlder 

 just mentioned, during the blast of the siren trumpet. 



At this station, during the visit of Sir Frederick Arrow, 

 the sound was lost in the direction of the axis of the trum- 

 pet at a distance of two miles, and then again regained with 

 distinctness at the light-vessel, a distance of four and one-half 

 miles; this was what I have denominated an abnormal phe- 

 nomenon, which was due as I think — to a slight variation 

 in the velocity of the lower and upper parts of the current of 

 air, but unfortunately, the demand for the use of the vessel 

 as a light-house tender prevented the attempt to ascertain 

 whether the same phenomenon would be observed a second 

 time, and to further investigate its cause. 



Observations September 1, 1874. — The second series of inves- 

 tigations this season was made with General J. G. Barnard, 

 of the Light-House Board, and General I. C. Woodruff, en- 

 gineer of the third district. We proceeded on this occasion 

 in the steamer Mistletoe to Block Island, — one of the outer 

 stations of the Light-House Board, fully exposed (without 

 intervention of land) to the waves and storms of the ocean. 



