REPORT OF THE SECRETARY. 43 



that which results from the consciousness of having labored somewhat 

 successfully in advancing the efficiency of a service which is one of 

 the benevolent institutions of the present day tending to facilitate the 

 harmonious intercourse of nations widely separated by intervening 

 oceaus. 



During the last summer I devoted the entire vacation to the investi- 

 gation of sound in its relation to fog-signals, the results of which have 

 been published in the report of the Light-House Board for 1875. These 

 investigations were a continuation of those of former years, and tend 

 to establish the facts previously obtained, as well as to extend tuo 

 knowledge of the phenomena of sound in its application to the uses of 

 the mariner. 



In these investigations the following conclusions have been arrived 

 at: 



1. That the rays of a beam of sound do not, like those of a beam of 

 light, move parallel to each other from the surface of a concave reflector, 

 but constantly diverge laterally on all sides, and although at first they 

 are more intense in the axis of the reflector, they finally spread out so 

 as to encompass the whole horizon, thus rendering the use of reflectors to 

 enforce fog-signals of little value. 



2. That the effect of wiud in increasing or diminishing sound is not 

 confined to currents of air at the surface of the earth, but that those of 

 higher strata are also active in varying its transmission. 



3. That although sound is generally heard farther with the wind than 

 against it, yet in some instances the reverse is remarkably the case. 



4. That sound may be heard in some cases at a greater distance, 

 while it is inaudible at a less distance from its origin. 



5. That a distant sound may be heard at the top of a tower in some 

 cases when it is inaudible at the bottom. 



6. That sound experiences a refraction deflecting it, in some cases, in 

 a horizontal direction, and in others in a vertical plane, which explains 

 most of the phenomena above-mentioned. 



The results obtained have excited considerable interest in this coun- 

 try and in Europe, and have given rise to criticism and discussions 

 which will tend to enlarge and diffuse the knowledge of this important 

 subject. 



I have also, in behalf of the Light-House Board, made a series of 

 experiments on petroleum as a light-house illuminaut. These experi- 

 ments were in continuation of those which I had previously made in 

 regard to the introduction of lard-oil. Previous to the establishment of 

 the Light-House Board, sperm-oil had been exclusively used in our 

 system of light-houses, but the expense of this gradually increased from 

 year to year until it became as high as $3 per gallon. After a laborious 

 series of experiments, it was found that, under certain conditions, lard-oil 

 might be substituted, and as this could be purchased at the time for 

 from 50 to GO cents per gallon, a saviug of more than a hundred thousand 

 dollars per annum was the result of the change. At the same time, a 



