492 WRITINGS OF JOSEPH HENRY. [1877 



So well established was the phenomenon, that General 

 Duane attempted to remedy the evil by elevating the dupli- 

 cate whistle (with which every station is provided) to a 

 height twenty-two feet above the level of the other whistle, 

 by placing it on the upper end of a tube. But this arrange- 

 ment produced no beneficial effect. 



September 4, 1877. — In the morning of September 4, on 

 which we commenced our experiments, the weather was 

 clear, the wind west-southwest, the velocity from ten to 

 twelve miles, remaining nearly constant during the day. 

 Our first object was to verify by direct observation the 

 several features of the phenomenon, and for this purpose 

 we steamed to the southward, or directly to the wind- 

 ward, from the station through the region in which the 

 abnormal phenomena had been noticed. The pressure of 

 the atmosphere, as indicated by an aneroid barometer, 

 was 28'9 inches. The temperature of the air was 67*^ 

 Fahrenheit; that of the water at various points along 

 our course was 58°, except at two points where the ther- 

 mometer indicated 57°. This difference was too small to 

 have any perceptible effect on the density of the rapidly 

 moving air which was passing over the surface of the water. 

 As we increased our distance from the signal the sound 

 slightly diminished in loudness until the distance was 

 between a quarter and half a mile, when it suddenly ceased 

 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 position of the station could be located with facility; but 

 on proceeding farther in the same direction it appeared to 

 diminish gradually except at one point, when a blast, as 

 indicated by the steam issuing from the whistle, was inaudi- 

 ble ; 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 



