RESEARCHES IN SOUND. 547 



to be heard, and continued inaudible through a distance of about a mile, 

 when it was faintly heard and continued to increase in loudness until we 

 reached the distance of four miles ; at this point it was heard with such 

 clearness that the i)Osition of the station could be located with facility ; 

 but on proceeding farther in the same direction it ajjpeared to diminish 

 gradually except at one point, when a blast, as indicated by the steam 

 issuing from the whistle, was inaudible; but on turning the vessel around 

 the next blast was distinctly heard. 



As a second experiment we retraced the same line back to the station 

 and observed the same phenomena in a reverse order. The sound was 

 heard the loudest at a point four miles from the station ; afterward it 

 diminished and then became inaudible through a space of two miles, 

 and then suddenly burst forth nearly in full intensity at the distance of 

 a quarter of a mile, and continued loud until the station was reached. 



As a third experiment the same line was traversed again, the only 

 difference in the condition of the exj)eriment being that the whistle on 

 the steamer was sounded every minute between the blasts of the signal 

 at the station ; and while the observers on the vessel noted the sounds 

 from- the latter, those at the station observed the sound from the former. 

 The same phenomena as described in the previous experiments were 

 witnessed by those on board the vessel, but on receiving the report of 

 the observers at the station, it was found that no cessation of the sound 

 from the steamer was observed through the whole distance traversed by 

 the vessel. It should be noted that the whistle at the station is ten 

 inches in diameter, actuated by a pressure of sixty pounds of steam, 

 and that on board the vessel six inches in diameter with twenty-five 

 pounds of steam. It appears from this remarkable result that a feeble 

 sound passes freely through what has been called the region of silence 

 when sent in the direction of the motion of the wind, when a louder 

 sound does not jiass in the ojiposite direction. 



As a fourth experiment the vessel proceeded northward on the oppo- 

 site side of the station to that before traversed, but in the prolongation 

 of its previous course. The sound in this case from the signal to the 

 observers on the vessel was with the wind, while that from the vessel 

 to the observers at the station was against the wind. In this experi- 

 ment no cessation was observed on the vessel in the hearing of the 

 sound from the station ; it was heard with varying intensity to the dis- 

 tance of four and a half miles, and could probably have been heard 

 much farther had our progress not been interrupted by land. On return- 

 ing to the station the observers there reported that after the vessel had 

 left the station and was scarcely more than a hundred yards distant not 

 a single blast of its whistle was heard. In this case 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 



