426 WRITINGS OF JOSEPH HENRY. [1874 



PART III.— INVESTIGATIONS DURING 1873 AND 1874. 

 (Report of the United States Light-House Board for 1874, pp. 107-117.) 



Observations on Sound and Fog-Signals in August, 1873. 



Professor Henry, chairman, and Commander John G. 

 Walker, naval secretary, of the Light-House Board, left Port- 

 land August 12th, 1873, at 3 o'clock p. m. in the steam-tender 

 Myrtle, Captain Foster, for Whitehead light-station, at which 

 place abnormal phenomena of sound had been observed. 



Whitehead light-station is on a small island about a mile 

 and a half from the coast of Maine, on the western side of 

 the entrance to Penobscot Bay, and in the direct line of the 

 coasting-steamers and other vessels from the westward, — 

 bound into the Penobscot Bay and river. The light-house 

 and fog-signal are situated on the south-east slope of the 

 island, the surface of which consists almost entirely of rock, 

 the middle being at an elevation of 75 feet above the mean 

 tide-level. 



The phenomena which had been observed at this and 

 other stations along the coast consisted of great variation of 

 intensity of sound while approaching and receding from the 

 station. As an example of this we may state the experience 

 of the observers on board the steamer City of Richmond on 

 one occasion, during a thick fog at night in 1872. The ves- 

 sel was approaching Whitehead from the south-westward, 

 when at a distance of about six miles from the station, the 

 fog-signal — which is a 10-inch steam-whistle, was distinctly 

 perceived and continued to be heard with increasing inten- 

 sity of sound until within about three miles, when the sound 

 suddenly ceased to be heard, and was not perceived again 

 until the vessel approached within a quarter of a mile of the 

 station, although from conclusive evidence furnished by the 

 keeper, it was shown that the signal had been sounding dur- 

 ing the whole time. The wind during this time was from 

 the south, or approximately in an opposite direction to the 

 sound. Another fact connected with this occurrence was that 

 the keeper on the island distinctly heard the sound of the 



