520 WRITINGS OF JOSEPH HENRY. [1877 



the coast of Maine, at the entrance of Penobscot Bay. It was 

 reported as having been frequently experienced by the cap- 

 tains of the steamers plying between Boston and New 

 Brunswick, and it had also been observed on two different 

 occasions by officers of the light-house establishment. 



The phenomenon, as reported by these authorities, con- 

 sisted in hearing the sound of a ten-inch whistle distinctly 

 as the station is approached till within the distance of from 

 four to six miles, then losing it through a space of about 

 three miles, and not hearing it again until within about a 

 quarter of a mile from the instrument, when it suddenly be- 

 comes audible almost in its full power. 



This phenomenon — according to the statement of the 

 keeper of the light-house station, is noticed whenever the 

 vessel is approaching the station from the south-west, and the 

 wind is in the same direction. It is especially observed dur- 

 ing a fog (when the warning of the signal is most wanted), 

 and this is here always accompanied by a wind from the 

 south or southwest. 



Our first object was to verify the phenomenon, and for 

 this purpose we steamed to the south-west, directly against 

 the wind, which was blowing at the time with a velocity of 

 about ten miles per hour ; this fortunately happened to be 

 the direction of the wind during which the phenomenon was 

 most frequently observed. The whistle was sounded every 

 minute by an automatic arrangement, and the time at which 

 the several blasts were given could be noted from the vessel 

 by the puffs of steam emitted by the whistle. As we increased 

 our distance from the signal the sound very slightly dimin- 

 ished in loudness until the distance was about a half mile, 

 when it suddenly ceased to be heard, and continued inaudi- 

 ble for about a mile farther, when it was faintly heard, and 

 continued to increase in loudness until we reached the dis- 

 tance of four miles; at this point it was heard with such 

 clearness that the position of the station could be readily 

 located in the densest fog, but on proceeding still farther in 

 the same direction it gradually diminished and was finally 

 again lost. 



