POPULAR SCIENCE 



627 



silent zone varies from 28 miles at the western end to 48 miles 

 close to the eastern coast, while the outer margin of the zone is 

 comprised between distances of 65 and 95 miles from the source. 

 Over the greater part of the sound-area, the air was either still 

 or there was a light wind from the north-east. 1 



The sound-areas of a very different kind of explosion are 

 represented in the remaining map, Fig. 3. From the plateau 

 which occupies the centre of the main island of Japan rises 



i°IlotVtngnaa 

 \ 



Upplngnaa" 



nor champ ton 



Fig. 2. 



Sound-areas of East London explosion, January 19, 19 17. 



the Asamayama, one of the greatest of Japanese volcanoes. Its 

 return to activity during the present century, after a long in- 

 terval of quiescence, has been distinguished by a series of ex- 

 plosions, the loudest of which are heard for a hundred miles or 

 more from the volcano. In the explosion of December 25, 

 1 910, the double sound-area was noticed for the first time in 



1 " The Sound-waves and other Air-waves'of the East London Explosion 

 of January 19, 1917," Edinburgh Royal Society Proceedings, vol. xxxviii, 1918, 

 PP- IJ 5 -2 9 ; see also the Quarterly Review for July 1917, pp. 51-60. 



