EESEAKCIIES IN SOUND. 481 



in meclianism, was well qualified for the work. The assignment of this 

 duty to General Duane by the Light-House Board was made diu-ing my 

 absence in Europe, in 1870, and as my vacation in 1871 was devoted to 

 light-house duty in California, I had no opportunity of conferring with 

 him on the subject until after his exi^eriments were completed. His re- 

 sults are therefore entirely independent of those obtained under my di- 

 rection, and I give them herewith in his own words, with such com- 

 ments as they may suggest and as are necessary to a i^roper elucidation 

 of the subject. 



EXPERIIIENTS AT PORTLAND, ME. 1871, BY GENERAL DUANE. 



The apparatus employed consisted of the first-class siren, first-class Daboll trumpet 

 and steam-whistles of various sizes. 



The ])oints to ho decided were : 



1st. The relative jjower of these machines ; i. e., the distances at which they could be 

 heard under various conditions of the atmosphere. 



2d. The amount of fuel and Avater consumed by each. 



3tl. The attention and skill required in oi^erating them. 



4th. Their endurance. 



5th. Whether they are sufficiently simple in construction to permit of their being 

 managed and kept in running order by the class of men usually appointed light- 

 house keejiers. 



In conducting these experiments the following method was pursued : 



The signals were sounded at alternate minutes, and their sound compared at dis- 

 tances of two, three, and four miles, and from different directions. On every occasion 

 the quantity of fuel and water consumed per hour by each was carefully noted, and 

 the condition of each machine examined, both before and after the trial,' to ascertain 

 whether any of its parts had sustained injnry. 



Before giving the results of these (jxperiments some facts should be stated, which 

 will explain the difficulty of determining the power of a fog-signal. 



There are six steam fog-whistles on the coast of Maine ; these have been frequently 

 heard at a distance of twenty miles, and as frequently cannot be heard at the distance 

 of two miles, and this with no perceptible difference in the state of the atmosphere. 



The signal is often heard at a great distance in one direction, while in another it 

 will be scarcely audible at the distance of a mile. This is not the effect of wind, as 

 the signal is frequently heard much farther against the wind than with it. For ex- 

 ample, the whistle on Cape Elizabeth can always 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. 



[In this sentence, General Duane certainly does not intend to convey 

 the idea that a signal is frequently heard "at a much greater distance 

 against the wind than with it," since this assertion would be at variance 

 with the general experience of mankind; but the word "frequently" 

 applies to the whistle on Cape Elizabeth, which has been already men- 

 tioned as a remarkably exceptional case, in which the sound is heard 

 best against the wind during a northeast scow-storm.] 



The most perplexing difficulty, however, arises from the fact that the signal often 

 appears to be surrounded by a belt, varying ni radius from one to one and a half miles, 

 from which the sound appears to be entirely absent. Thus, in moving directly from 

 a atatioai, the sound is audible for the distance of a mile, is then lost for about the 

 same distance, after which it is again distinctly heard for a long time. This action is 

 common to all eai-siguals, and has been at limes observed at all the stations, at one 

 of which the signal is situated on a bare rock twenty miles from the main-land, with 

 no surrounding objects to afi"ect the sound. 



All attempts to re-enforce the sound by means of reflectors have hitherto been un- 

 successful. Upon a large scale, sound does not appear, on striking a surfa,ce, to be 

 reflected after the ;nannor of light and heat, but to roll along it like a cloud of smoke. 

 S. Mis. 59 31 



