1874] WRITINGS OF JOSEPH HENRY. 377 



ment alone of the fog-signals in ordinary use, but directed a 

 series of experiments in order to improve this branch of its 

 service. For this purpose the board employed Prof. J. H. 

 Alexander, of Baltimore, who made a report on the subject, 

 which was published among the documents. The investiga- 

 tions of Professor Alexander related especially to the use of 

 the locomotive steam-whistle as a fog-signal, and in his re- 

 port he details the results of a series of experiments in regard 

 to the nature and adjustment of the whistle, the quantity 

 of steam necessary to actuate it, with suggestions as to 

 its general economy and management. He found, what 

 has since been fully shown, that the power of the sound 

 depends upon the pressure of the steam in the boiler, and 

 the pitch upon the distance between the circular orifice 

 through which the steam issues, and the edge of the bell. 

 He appears however to be under an erroneous impression 

 that the sound is produced by the vibrations of the metal of 

 the goblet or bell, while in fact this latter portion of the 

 apparatus is a resounding cavity, which as I have shown in 

 subsequent experiments, may be constructed of wood as well 

 as of brass, in order to produce the same effect. Prof. Alex- 

 ander also mentions the effect of the wind in diminishing 

 the penetrating power of sound when in an adverse direction, 

 either directly or approximately. He also recommends the 

 adoption of an automatic pump to supply the boilers with 

 water, and also to open and shut the valves at the proper 

 intervals for blowing the whistle. He states that the loca- 

 tion of a sound can be determined more precisely in the case 

 of loud, high sounds than in that of feebler or lower ones. 

 I am not prepared to concur with him on this point, in view 

 of experiments of my own. In all cases however loud sounds 

 are more desirable than feebler ones, in order that they ma}'' 

 be heard at a greater distance above the noise of the surf 

 and that of the wind as it passes through the spars and rig- 

 ging of vessels. 



The board at this time however was not prepared to 

 adopt these suggestions, and an unsuccessful attempt to use 

 a steam-boiler, rendered abortive by the incapacity of the 



