404 WRITINGS OF JOSEPH HENRY. [1874 



Experiments at Portland, Me., 1871, by General James C. Duane. 



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

 trumpet, and steam-whistles of various sizes. 



The points to be decided were : 



1st. The relative power 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 water consumed by each : 



3d. The attention and skill required in operating 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 ap- 

 pointed light-house keepers. 



In conducting these experiments the following method was pursued : 



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

 at distances 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 be- 

 fore and after the trial, to ascertain whether any of its parts had sustained 

 injury. 



Before giving the results of these experiments 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 an- 

 other it will be scarcely audible at the distance of a mile. This is not the 

 eflect of wind, as the signal is frequently heard much farther against the 

 wind than with it. For example, the whistle on Gape Elizabeth can always 

 be distinctly heard in Portland, — a distance of nine miles, during a heavy 

 north-east snow-storm, the wind blowing a gale directly from Portland to- 

 ward 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 experi- 

 ence of mankind ; but the word " frequently " applies to the 

 whistle on Cape EUzabeth, which has been already men- 

 tioned as a remarkably exceptional case, in which the sound 

 is heard best against the wind during a north-east snow- 

 storm. 



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

 often 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. Thus 

 in moving directly from a station, the sound is audible for the distance of a 

 mile, is tlien lost for about the same distance, after which it is again dis- 

 tinctly heard for a long time. This action is common to all ear-signals, and 

 has been at times 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 surround- 

 ing objects to affect the sound. 



AH attempts to re-enforce the sound by means of reflectors have hitherto 

 been unsuccessful. Upon a large scale, sound on striking a surface does not 



