EESEAECHES IN SOUND. 511 



We are farther confirmed in our conclusion by the publication of an 

 interesting i^aper in the proceedings of the Eoyal Society- by Professor 

 Osborne Eeynolds, of Owens College, Manchester, intended to show that 

 sound is not absorbed by the condition of the atmosphere, but refracted 

 in a, manner analogous to the hypothesis which has been adopted in the 

 preceding report. 



Much further investigation is required to enable us to fully under- 

 stand the effects of winds on the obstruction of sound, and to determine 

 the measure of the effect of variations of density in the air due to in- 

 equality of heat and moisture. But such investigations can only be 

 made under i^eculiar conditions of weather and favorable localities, with 

 the aid of a number of steamers, and a series of observers, by whom the 

 transmissibility of the air may be simultaneously observed in different 

 directions. The position which we were so fortunate to obtain in our 

 experiments in the lower bay of New York at the season of the prev- 

 alence of land and sea breezes was exceptionally favorable for the study 

 of the action of wind upon sound. It is the intention of the Light- 

 House Board to continue observations in regard to this matter, an3 to 

 embrace every favorable opportunity for their prosecution under new 

 and varied conditions. 



Light-House Board, October, 1874. 



PAET IV.— INVESTIGATIONS IN 1875.* 

 Prelijvidtary Eemarks. 



In the Appendix to the Light-House Eeport of 1874 1 gave an account 

 of a series of investigations relative to fog-signals, which had been made 

 at difierent times under the direction of the chairman of the committee 

 on experiments. 



These investigations were not confined to the instruments for produc- 

 ing sound, but included a series of observations on sound itself, in its 

 application to the uses of the mariner. In the course of these investiga- 

 tions the following conclusions were early arrived at : 



1st. That the rays of a beam of loud sound do not, like those 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 si)read out so as to 

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

 enforce sound for fog-signals of little value. 



2d. That the effect of wind 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. 



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

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



* From tlie Eejiort of tlie Light-House Board, for 1875. 



