548 THE POPULAR SCIENCE MONTHLY. 



An interval of 12 hours sufficed to change iu a surprising degree 

 the acoustic transparency of the air. On the 1st of July the sound 

 had a range of nearly 13 miles ; on the 2d the range did not exceed 

 4 miles. 



Contradictory Results. Thus far the investigation proceeded 

 with hardly a gleam of a principle to connect the inconstant results. 

 The distance reached by the sound on the 19th of May was 3^ miles ; 

 on the 20th it was 5^ miles ; on the 2d of June, 6 miles ; on the 3d, 

 more than 9 miles ; on the 10th it was also 9 miles ; on the 25th it fell 

 to 6^ miles ; on the 26th it rose again to more than 9^ miles ; on the 

 1st of July, as we have just seen, it reached 12f, whereas on the 2d 

 the range shrunk to 4 miles. None of the meteorological agents ob- 

 served could be singled out as the cause of these fluctuations. The 

 wind exerts an acknowledged power over sound, but it could not 

 account for these phenomena. On the 25th of June, for example, 

 when the range was only \ miles, the wind was favorable ; on the 

 26th, when the range exceeded 9^ miles, it was opposed to the sound. 

 Nor could the varying optical clearness of the atmosphere be invoked 

 as an explanation; for, on July 1st, when the range was 12f miles, a 

 thick haze hid the white cliffs of the Foreland, while on many other 

 days, when the acoustic range was not half so great, the atmosphere 

 was optically clear. Up to July 3d all remained enigmatical ; but on 

 this date observations were made which seemed to me to displace sur- 

 mise and perplexity by the clearer light of physical demonstration. 



Solution op Contradictions. On July 3d we first steamed to a 

 point 2.9 miles southwest-by-west of the signal station. No sounds, 

 not even the guns, were heard at this distance. At two miles they 

 were equally inaudible. But this being a position at which the sounds, 

 though strong in the axis of the horn, invariably subsided, we steamed 

 to the exact bearing from which our observations had been made on 

 July 1st. At 2.15 p. m., and at a distance of 3f miles from the station, 

 with calm, clear air and a smooth sea, the horns and whistle (Ameri- 

 can) were sounded, but they were inaudible. Surprised at this result, 

 I signaled for the guns. They were all fired, but, though the smoke 

 seemed at hand, no sound whatever reached us. On July 1st, in this 

 bearing, the observed range of both horns and guns was 10^ miles, 

 while, on the bearing of the Varne light-vessel, it was nearly 13 miles. 

 We steamed in to 3 miles, paused, and listened with all attention ; 

 but neither horn nor whistle was heard. The guns were again sig- 

 naled for ; five of them were fired in succession, but not one of them 

 was heard. We steamed on in the same bearing to 2 miles, and had 

 the guns fired point-blank at us. The howitzer and the mortar, with 

 3-lb. charges, yielded a feeble thud, while the 18-pounder was wholly 

 unheard. Applying the law of inverse squares, it follows that, with 

 the air and sea, according to accepted notions, in a far worse condi- 



