W. B. Taylor — Recent Researches in Sound. 35 



two miles, with apparently the same state of the atmosphere. 

 (L. H. Rep., p. 100.) 



[B.] The signal was often heard at a great distance in one 

 direction, while scarcely audible at a mile in another direction, 

 and this quite irrespective of the wind. (p. 100.) 



[C] Falling snow was observed not to obstruct sound sensi- 

 bly, as the steam-whistle on Cape Elizabeth can be "distinctly 

 heard in Portland, a distance of nine miles, during a heavy 

 northeast snow-storm, the wind blowing a gale directly from 

 Portland toward the whistle." (p. 100.) 



[D.] The signal station frequently " appears to be surrounded 

 by a belt varying in radius from one to one and a half miles, 

 from which the sound appears to be entirely absent." Receding 

 from the signal, its sound may be audible for the distance of a 

 mile, then lost for the distance of a second mile, and then au- 

 dible again for a much farther distance. This abnormal phe- 

 nomenon has been observed at various stations, and at one 

 where the signal is on a bare rock in mid-ocean, twenty miles 

 away from land, and with no surrounding objects to affect the 

 sound, (p. 100.) 



No observations have been made to show that this occasional 

 sound-chasm is really a "belt" entirely surrounding the signal ; 

 a supposition which appears to be antecedently improbable, 

 and one which would require a large number of radiating ob- 

 servations made simultaneously, to establish it. The curious 

 and exceptional fact, however, is confirmed by the observations 

 of Henry [8] made subsequently. 



[E.] Confirmatory of Henry [1], General Duane found that a 



whistle in the focus of a large parabolic reflector, though giving 



a notably louder sound in front near the reflector, yet at the 



distance of a few hundred yards, had its beam of sound so 



spread that the acoustic shadow behind the mirror vanished, 



and no perceptible difference appeared. A wooden trumpet or 



square pyramidal box 20 feet long, in a horizontal position 



with the whistle in the smaller end, gave, however, more suc- 



co:s?fiil results, the increase of sound in the open axis being 



T.o>ceptible at the distance of a mile. (Rep., p. 103.) This cor- 



iids also with Henry's observation [7]. 



1 In repetition and explanation of observation [A] General 



>' remarks: "It frequently occurs that a signal which 



r ordinary circumstances would be audible at the distance 



: 'en miles, cannot be heard from a vessel at the distance 



-ingle mile. This is probably due to the reflection men- 



l by Humboldt." (p. 104.) This great traveller and scien- 



bserver, in his graphic narrative of exploration in the 



i-n part of South America published at the beginning of 



utury, ascribes the diminished audibility during the day, 



