POPULAR SCIENCE 



THE SILENT ZONE IN EXPLOSION 



SOUND-AREAS 



By CHARLES DAVISON, Sc.D., F.G.S. 



Various explosions during the present century have revealed 

 a phenomenon which has an important bearing on the mode in 

 which sound is transmitted by the atmosphere. In some great 

 explosions, though not in all, the sound-area consists of two 

 detached portions. One portion, the inner sound-area, sur- 

 rounds the source of sound. The other, the outer sound-area, 

 is at its nearest point from fifty to a hundred miles or more from 

 the source. Between them lies a tract — the silent zone — within 

 which the sound is rarely or never heard. 



The accompanying maps will give some idea of the forms and 

 positions of these sound-areas. In each map, the source of 

 sound is indicated by a small cross, and the boundaries of the 

 sound-areas are represented by the dotted lines. 



Fig. i represents the silent zone and outer sound-area of the 

 minute-gun fired at Spithead on February i, 1901, when Queen 

 Victoria's body was borne from the Isle of Wight to Portsmouth. 

 Owing to the general absence of observations from the sea- 

 covered district, no attempt can be made to map the inner 

 sound-area. Its boundary, however, certainly passed within 

 a very few miles — possibly within one mile — to the north of 

 the line of battleships. Then, still farther to the north, there 

 lay the broad silent zone, within which not a sound of the re- 

 ports was heard. Indeed, the nearest point on land at which 

 they were recorded is fifty miles from Spithead. From this 

 point, there spreads outwards the great outer sound-area, the 

 sullen booms being unusually loud from sixty to ninety miles 

 from Spithead. Even more than a hundred miles away, the 

 reports were noticeable, the greatest distance being 139 miles 

 towards the north-east. In the south of Hampshire, the wind 

 at the time was mainly from the shore ; in the outer sound-area, 



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