RESEARCHES IN SOUKD. 499 



tween the whistle and observer was entirely unobstructed by the side 

 of the trumpet, when the sound was apparently as loud as in the pro- 

 longation of the axis itself. On the west side of the axis of the trumpet 

 the sound in a like manner diminished from the axis until the prolonga- 

 tion of the side of the trumpet was reached, when it became feeble 

 again, slightly increased, and then gradually diminished until the lin« 

 of direc.ion made an angle of about 80^ with the axis of the trumpet, 

 when it ceased to be heard at a distance of about one and a half miles. 

 It should bo observed, however, that at this point the line of sight of 

 the observers was obstructed by the side of the trumpet and the smoke- 

 stack of the boiler. The wind was light, at south-southwest, api)roxi- 

 mately in direct opposition to the direction of the sound when it ceased 

 to be heard. We are informed that complaints had previously been made 

 by officers of steamers passing near this point that the sound was here 

 inaudible previous to the introduction of this trumpet ; it would there- 

 fore follow that it is of no use in increasing the effect on the western 

 side of the axis and is of injury to the sound on the lines of i^rolonga- 

 tion of its sides. If the sound ceased to be heard at the point mentioned, 

 when the trumpet is removed the only api^areut cause of the phenome- 

 non will be the prevailing direction of the wind, which, coming from the 

 southwest, will be in opposition to the sound of the whistle; but in the 

 case of the i^resent investigation the force of the wind was so small that 

 it scarcely appeared adequate to produce the effect, and this question, 

 therefore, must be left for further investigation. It may be important 

 to state that in the case where the sound ceased to be heard it was re- 

 gained by sailing directly toward the station about one mile, or at half 

 a mile from the station. After making the foregoing observations as to 

 the intensity of sound in different directions from the station, the obser- 

 vations were closed by sailing directly along the axis of the trumpet 

 until the sound, which gradually grew fainter as the distance increased, 

 finally ceased to be heard at a distance of about nine miles. In com- 

 ])aring this last result with an instrument of about the same power at 

 Whitehead, which gave a i)erceptible sound at a distance of fifteen 

 miles, the only aj)parently variable circumstance was the velocity of the 

 wind, in both cases adverse to the direction of the sound ; but in that 

 of Cape Elizabeth it was of considerable more intensity. 



During the foregoing experiments, when the vessel was about a mile 

 from the station, steaming directly outward, in the prolongation of the 

 axis of the instrument, there was heard after each sound of the whistle 

 a distinct echo from the broad, unobstructed ocean, which was attributed 

 at the time, as in other cases, to reflections from the crests and hoEows 

 of the waves, a similar phenomenon having since been referred to a re- 

 flection from air of a different density. This observation becomes im- 

 portant in regard to the solution of the question as to the abnormal 

 phenomena of sound. 



