1877] WRITINGS OF JOSEPH HENRY. 493 



miles from the station ; afterward it diminished and then 

 became inaudible through a space of two miles, and then 

 suddenly burst forth in nearly 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 experiment 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 sounds from the former. 

 The same phen-omena as described in the previous experi- 

 ments 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 pouiids of steam. It appears from this remark- 

 able result that a feeble sound passes freely through what 

 has been called the region of silence when sent in the direc- 

 tion of the motion of the wind, when a louder sound does 

 not pass in the opposite direction. 



As a fourth experiment, the vessel proceeded northward 

 on the side of the station opposite "to that before traversed, 

 but in the prolongation of its previous course. The sound 

 from the signal to the observers on the vessel was in this 

 case with the wind, while that from the vessel to the obser- 

 vers 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 w^as heard with varying 

 intensity to the distance of four and a half miles, and could 

 probably have been heard much farther had our progress 

 not been interrupted by land. On returning to the station 

 the observers there reported that after the vessel had left the 

 station, and was scarcely more than a hundred yards dis- 

 tant, not a single blast of its whistle was heard. In this case 



