504 EESEARCHES IN SOUND. 



at various stations, at wliich the trumpet or siren lias been used, to the 

 reflection of the sound from the crests and slopes of the waves, and the 

 observation we have mentioned would appear to favor this hypothesis. 

 In connection with this explanation, I may mention that my attention 

 has been called by General Meigs, of the United States Army, tx» an 

 echo from the palings of a fence, and also from a series of indentations 

 across the uoder side of the arch of one of the aqueduct bridges of the 

 Washington water- works. The fact that the sound was much louder at 

 a point considerably distant from the trumpet was noted by one of the 

 I)arty entirely unacquainted with the hypothesis. 



The keeper at this station confirmed without a leading question the 

 statement of Captain Keeney, that it frequently happens that a feeble 

 sound of a distant object, as the roar of the surf, can be heard against 

 the direction of the wind, and that in this case it always betokens a 

 change in the weather, and is, in fact, used generally by the fishermen 

 as a prognostic of a change in the direction of the wind, which will, in 

 the course of a few hours, invariably spring up from an opposite quar- 

 ter. In such case, it is highly probable, as has been stated, that a change 

 has already taken x)lace in the direction of the upper strata of the air, 

 although, from theoretical considerations, we might infer that the same 

 result would be produced if the wind were stationary above and moving 

 with a considerable velocity in a direction opposite to the sound at the 

 surface of the earth, the velocity gradually diminishing as we ascend, 

 for in this case, also, the inclination of the sound waves would be down- 

 ward. 



The third series of investigations, September 23, 24, 1874, was made 

 in company with Captain John Davis and Major Hains, both of the 

 Light-House Board, and General Woodruff, engineer of the third dis- 

 trict, and Mr. Brown, patentee of the siren. For the purpose three 

 light-house tenders were employed, viz: Mistletoe, Cai)tain Keeney 5 

 Putnam, Captain Field; Cackis, Captain Latham. 



The place of operation chosen for the first day's series was about 1^ 

 miles from the northern point of Sandy Hook. 



From the experience gained by the accumulated observations which 

 had been made, it was concluded that the phenomena of sound in re- 

 gard to perturbing influences could not be properly studied without 

 simultaneously observing the transmission of sound in opposite direc- 

 tions. It was therefore concluded to emx^loy at least two steamers in 

 making the investigations. 



In regard to this point the commission was fortunate in being able to 

 command the use, for a limited period, of the three tenders mentioned 

 above, which happened to be at the time assembled at the light-house 

 depot, Staten Island, and could be spared from their ordinary opera- 

 tions for a few days without detriment to the service. It was also for- 

 tunate in selecting for the scene of the investigations an unobstructed 



