THE ATMOSPHERE AND FOG-SIGNALING. 547 



due to any variation on the part of the instruments, but purely to the 

 changes of the medium traversed by the sound. What these changes 

 were shall be indicated subsequently. 



The range of our best horns on June 10th was 8f miles. The guns 

 at this distance were very feeble. That the loudness of the sound 

 depends on the shape of the gun was proved by the fact that thus far 

 the howitzer, with a three-lb. charge, proved more effective than the 

 other guns. 



On June 25th a gradual improvement in the transmissive power of 

 the, air was observed from morning to evening ; but at the last the 

 maximum range was only moderate. The fluctuations in the strength 

 of the sound were remarkable, sometimes sinking to inaudibility and 

 then rising to loudness. A similar effect, due to a similar cause, is 

 often noticed with church-bells. The acoustic transparency of the 

 air was still further augmented on the 26th : at a distance of 9^ miles 

 from the station the whistles and horns were plainly heard against a 

 wind with a force of four ; white on the 25th, with a favoring wind, the 

 maximum range was only 64- miles. Plainly, therefore, something else 

 than the wind must be influential in determining the range of the sound. 



On Tuesday, July 1st, observations were made on the decay of the 

 sound at various angular distances from the axis of the horn. As 

 might be expected, the sound in the axis was loudest, the decay being 

 gradual on both sides. In the case of the gun, however, the direction 

 of pointing has very little influence. 



The day was acoustically clear ; at a distance of 10 miles the horn 

 yielded a plain sound, while the American whistle seemed to surpass 

 the horn. Dense haze at this time quite hid the Foreland. At 104 

 miles occasional blasts of the horn came to us, but, after a time, all 

 sound ceased to be audible ; it seemed as if the air, after having been 

 exceedingly transparent, had become gradually more opaque to the 

 sound. 



At 4.45 p. M. we took the master of the Varne light-ship on board 

 the Irene. He and his company had heard the sound at intervals 

 during the day, although he was dead to windward and distant 12f 

 miles from the source of sound. 



Here a word of reflection on our observations may be fitly intro- 

 duced. It is, as already shown, an opinion entertained in high quar- 

 ters that the waves of sound are reflected at the limiting surfaces of 

 the minute particles which constitute haze and fog, the alleged waste 

 of sound in fog being thus explained. If, however, this be an efficient 

 practical cause of the stoppage of sound, and if clear, calm air be, as 

 alleged, the best vehicle, it would be impossible to understand how 

 to-day, in a thick haze, the sound reached a distance of 12f miles, 

 while on May 20th, in a calm and hazeless atmosphere, the maximum 

 range was only from 5 to 6 miles. Such facts foreshadow a revolution 

 in our notions regarding the action of haze and fogs upon sound. 



