546 THE POPULAR SCIENCE MONTHLY. 



knowledge, on record to prove that a sound once predominant would 

 not be always predominant, or that the atmosphere on different days 

 would show preferences to different sounds. On many subsequent 

 occasions, however, the sound of the horns proved distinctly superior 

 to that of the gun. This selective pow T er of the atmosphere revealed 

 itself more strikingly in our autumn experiments than in our summer 

 ones ; and it was sometimes illustrated within a few hours of the same 

 dav ; of two sounds, for example, one might have the greatest range 

 at 10 a. M., and the other the greatest range at 2 p. m. 



In the experiments on May 19th and 20th the superiority of the 

 trumpets over the whistles was decided ; and, indeed, with few excep- 

 tions, this superiority was maintained throughout the inquiry. But 

 there were exceptions. On June 2d, for example, the whistles rose in 

 several instances to full equality with, and on rare occasions subse- 

 quently even surpassed, the horns. The sounds were varied from clay 

 to day, and various shiftings of the horns and reeds were resorted to, 

 with a view of bringing out their maximum power. On the date last 

 mentioned a single horn was sounded, two were sounded, and three 

 were sounded, together ; but the utmost range of the loudest sound, 

 even with the paddles stopped, did not exceed 6 miles. With the 

 view of concentrating their power, the axes of the horns had been 

 pointed in the same direction, and, unless stated to the contrary, this 

 in all subsequent experiments was the case. 



On June 3d the three guns already referred to were permanently 

 mounted at the South Foreland. They were ably served by gunners 

 from Dover Castle. 



On the same day dense clouds quite covered the firmament, some 

 of them particulai-ly black and threatening, but a marked advance 

 was observed in the transmissive power of the air. At a distance of 

 6 miles the horn-sounds were not quite quenched by the paddle-noises ; 

 at 8 miles the whistles were heard, and the horns better heard; while 

 at 9 miles, with the paddles stopped, the horn-sounds alone were fairly 

 audible. During the clay's observations a remarkable and instructive 

 phenomenon was observed. Over us rapidly passed a torrential 

 shower of rain, which, according to Derham, is a potent damper of 

 sound. We could, however, notice no subsidence of intensity as the 

 shower passed. It is even probable that, had our minds been free 

 from bias, we should have noticed an augmentation of the sound, such 

 as occurred with the greatest distinctness on various subsequent occa- 

 sions during violent rain. 



The influence of " beats " was tried on June 3d, by throwing the 

 horns slightly out of unison ; but, though the beats rendered the sound 

 characteristic, they did not seem to augment the range. At a distance 

 from the station curious fluctuations of intensity were noticed. Not 

 only did the different blasts vary in strength, but sudden swellings 

 and fallings off, even of the same blast, were observed. This was not 



