C. GENERAL PHYSICS. 181 



siren seems to require the most, while the steam- whistle 

 gives the least trouble. As to the anomalies observed in 

 relation to the penetration and direction of sound from fog- 

 signals, General Duaue holds that they are to be attributed 

 mainly to the want of uniformity in the surrounding atmos- 

 phere, and that snow, rain, fog, and wind have much less in- 

 fluence than has generally been supposed. Rep. Light-house 

 Board, 1874, Appendix. 



fog-signals. 



In the appendix to the recent report of the Light-house 

 Board, Professor Henry gives the first account that has, as yet, 

 appeared of the experiments and observations made by him 

 in reference to fog-signals, and especially in reference to the 

 acoustic phenomena exhibited on a large scale in the atmos- 

 phere. Among other matters, he states that Professor Bache 

 adopted a very ingenious plan for an automatic fog-signal, 

 which consisted in taking advantage of a conical opening in 

 the rocky coast, generally designated as a blow -hole. On 

 the apex of this hole he erected a chimney, which was termi- 

 nated by a tube surmounted by a whistle. By this arrange- 

 ment a loud sound was produced as often as a wave entered 

 the mouth of the indentation. The penetrating power of the 

 sound was, under favorable circumstances, due to the press- 

 ure of a column of water twenty feet high, giving a press- 

 ure of about ten pounds to the square inch. The effect of 

 the percussion, however, sometimes added considerably to 

 this. In practice it was found that this arrangement, which 

 continued in operation for several years, did not entirely 

 supersede the necessity of occasionally producing sounds of 

 greater power. It is stated that Professor J. II. Alexander, 

 of Baltimore, in his investigations on the use of the locomo- 

 tive steam- whistles, experimentally demonstrated that the 

 power of the sound depends upon the pressure of the steam 

 in the boiler, and the pitch of the sound depends upon the 

 distance between the ed^-e of the whistle and the circular 



CD 



orifice through which the steam issues. Anions; the various 



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steam focr- signals, one consistinc: of a double whistle, im- 



*_* CD J CD 7 



properly called a steam gong, seems of interest. This con- 

 sists of two bells of the ordinary steam- whistle upon the 

 same hollow axes, mouth to mouth ; the upper bell has a 



