182 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tance of 3f miles from the station, with a calm air and a 

 smooth sea, the horns and whistle (American) 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 1, 

 in this bearing, the observed range of both horns and guns 

 was 10-J- 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 signaled for ; five of them 

 were fired in succession, but not one of them was heard. 

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

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

 with 3-pound charges, yielded a feeble thud, while the 18- 

 pourider was wholly unheard. Applying the law of inverse 

 squares, it follows that, with air and sea, according to accept- 

 ed notions, in far worse condition, the sound at 2 miles' dis- 

 tance on July 1 must have had more than forty times the 

 intensity which it possessed at the same distance at 3 P.M. 

 on the 3d. . . . 



" Humboldt, in his observations on the Falls of the Orino- 

 co, is known to have applied these principles to sound. He 

 found the noise of the falls far louder by night than by day, 

 though in that region the night is far noisier than the day. 

 The plain between him and the falls consisted of spaces of 

 grass and rocks intermingled. In the heat of the day ho 

 found the temperature of the rock to be considerably higher 

 than that of the grass. On every heated rock, he concluded, 

 rose a column of air rarefied by the heat; and he ascribed 

 the deadening of the sound to the reflections which it en- 

 dared at the limiting surfaces of the rarer and denser air. 

 This philosophical explanation, which admits of experiment- 

 al illustration in the laboratory, made it generally known 

 that a non -homogeneous atmosphere is unfavorable to the 

 transmission of sound. 



" But what on July 3, not with the variously heated plain 

 of Antures, but with a calm sea as a basis for the atmosphere, 

 could so destroy its homogeneity as to enable it to quench 

 in so short a distance so vast a body of sound? I here sub- 



J 



mit to the judgment of scientific men my own course of 

 thought regarding this question. As I stood upon the deck 



