430 WRITINGS OF JOSEPH HENRY. [1874 



the observations 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 comparing 

 this last result with an instrument of about the same power 

 at Whitehead, which gave a perceptible sound at a distance 

 of fifteen miles, the only apparently 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 considerably greater force. 



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 hol- 

 lows of the waves. A similar phenomenon has since been 

 elsewhere observed, and referred to a reflection from air of a 

 different density. This observation becomes important in 

 regard to the solution of the question as to the abnormal 

 phenomena of sound. 



Gape Ann Light-Station, Massachusetts, August 31, 1873. — 

 This is one of the most important stations on the New Eng- 

 land coast. It is furnished with two first-order lights and 

 a 12-inch steam whistle, actuated by 60 pounds pressure of 

 steam. The present is the fourth engine which has been 

 erected at this station, in consequence of the complaints either 

 as to the inefficiency of the sound or its failure to be heard 

 in certain directions. It was at first proposed to sail entirely 

 around the island in order to test the intensity of the sound 

 in different directions, but this was found impracticable on 

 account of the shallowness of water on the inland side; the 

 observations were therefore confined to the direction in 

 which complaints had been made as to the deficiency of the 

 signal, namely, in a southerly direction. The result of these 

 observations (the points of which included an arc of 120°) 

 was that the sound was heard with equal intensity except 

 when the direction of the station was to the northward and 



