502 EESEAECHES IN SOUND. 



trict, accompanied by Governor Ingersoll, of Connecticut, and Captain 

 Upshur, U. S. K. 



At this place are two sirens, tlie one to replace the other in case of 

 an accident. One of the sirens was sounded with the pressure of 50 

 pounds per square inch. The wind was across the axis of the trumpet, 

 and almost precisely at right angles to it. 



The steamer was headed against the wind, on a line at right angles 

 to the axis of the trumpet. The sound in this case also travelled against 

 the wind, which was at an estimated velocity of from 4 to 5 miles per 

 hour. The distance travelled before the sound became inaudible was 

 estimated, by the speed of the steamer, at 3.J miles. 



The steamer was next headed in an opposite direction and returned 

 along its previous path, across the mouth of the trumpet of the siren, 

 the sound gradually increasing in strength without any marked irregu- 

 larity, until the siren was reached, and on leaving this, the course re- 

 maining the same, the sound gradually diminished in intensity, but with 

 less rapidity than before, until it was finally lost at a distance of 7^ 

 miles. In the latter instance the movement of the sound was with the 

 wind. The result of these observations was conformable to that gene- 

 rally obtained from ijrevious observations, namely, that the sound is sel- 

 dom or never heard at the same distance in difierent 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 fre- 

 quently been observed in other investigations. It may be well to men- 

 tion that the siren trumpet at this locality is directed horizontally with 

 its prolonged axis passing over, immediately in front of the mouth of 

 the trumpet, a space of ^-ery rough ground, the surface of which is 

 principally composed of bowlders, one of which, of very large size, is 

 directly in front of the trumpet, and the idea occurred to me that this 

 rough surface might produce some eliect on the transmission of sound 

 to a distance. I observed by 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 trumpet 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 we have denominated 

 as an abnormal phenomenon, which we think was due to a slight varia- 

 tion in the velocity of the lower or upper part 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. 



The second investigations this season were September 1, 1874, with 

 General Barnard, of the Light- House Board, and General Woodruff, 



