376 WRITINGS OF JOSEPH HENRY. [1874 



was approaching, and as the wind during the fog at this 

 place is generally from the south, the steamer could be heard 

 five or six miles. The firing was continued as frequently as 

 the gun could be loaded until the steamer answered by a sig- 

 nal of three puffs of its whistle. The number of discharges was 

 from one to six, the latter exhausting a keg of powder valued 

 at $8. The keeper of the light-house acted as gunner with- 

 out compensation other than his salary. The cost of powder 

 was paid by the steamboat company. The report of the gun 

 was heard from two to six miles. 



This signal has been abandoned, — because of the danger 

 attending its use — the length of the intervals between the 

 successive explosions — and the brief duration of the sound, 

 which renders it difficult to determine with accuracy its 

 direction. 



The lamented General Hartman Bache, of the Light-House 

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

 signal which consisted in taking advantage of a conical open- 

 ing in the coast, generally designated a blow-hole. On the 

 apex of this hole he erected a chimney which terminated in a 

 tube surmounted by a locomotive 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 from this arrangement would not be great if it 

 depended merely on the hydrostatic pressure of the wave, 

 since this, under favorable circumstances, would not be more 

 than that of a column of water 20 feet high, giving a pres- 

 sure, of about 10 pounds to the square inch. The effect 

 however of the percussion might add considerably to this, 

 though the latter would be confined in effect to a single in- 

 stant. In regard to the practical result from this arrange- 

 ment, which was continued in operation for several years, it 

 was found not to obviate the necessity of producing sounds 

 of greater power. It is however founded on an ingenious 

 idea, and may be susceptible of application in other cases. 



Experiments by Professor J. H. Alexander, in 1855. 

 The Light-House Board was not content with the employ- 



