494 WRITINGS OF JOSEPH HENRY. [1877 



the phenomena which had been observed on the southerly 

 side of the station were exhibited in a reverse order on the 

 northerly side. 



In what may be considered the fifth experiment, the vessel 

 being at a distance of four miles from the station — on the 

 line traversed in the first two experiments, the sound was 

 slightly heard. The vessel then altered its course so as to 

 steam around the signal, keeping at the same distance until 

 the direction of the station, from the vessel, was nearly at right 

 angles to the direction of the wind ; at this point no sound 

 was heard from the station, although it had been slightly heard 

 at points along the curved line traversed in reaching the point 

 mentioned. The vessel then proceeded toward the station in 

 a straight line, but no sound was heard until it approached 

 the latter within a quarter of a mile. The observers at the 

 station however heard the sound from the vessel through the 

 wliole distance. 



This experiment was made to ascertain the truth of the 

 general impression that at this place the sound is heard better 

 coming at right angles — or across the wind, than in the direc- 

 tion in which it was blowing. The experiment however 

 was found in conformity with the general rule previously 

 established, that the sound was usually heard farthest with 

 the wind, least against the wind, and at an intermediate 

 distance across the wind. 



The primary object of these investigations has been to deter- 

 mine the mechanical causes to which the phenomena may 

 be referred, from which new conclusions may be deduced — 

 to be further tested by experiment, and such definite views 

 obtained, as may be of value in the employment of fog-signals 

 for the uses of the mariner. 



For this purpose a number of different hypotheses may 

 be provisionally adopted, and each compared with the actual 

 facts observed. 



The first hypothesis which had been suggested for the 

 explanation of the phenomena in question was that they are 

 due to some configuration of the land; but on inspecting the 

 Coast-Survey chart of this region it will be seen that the 



