628 



SCIENCE PROGRESS 



Japan. Both areas, it will be seen from Fig. 3, are elongated 

 from north to south, the Asamayama itself being close to the 

 western boundary of the inner area. The distance from the 

 volcano of the nearer margin of the outer area is 54 miles. ' 



Properties of the Silent Zone 



(1) As a rule, the silent zone is free from all sound of the 

 explosion, but, here and there within it, there may be places at 

 which the reports are heard by one or more persons. The 

 silent zone is then, strictly speaking, a zone of diminished 



Fig. 3. 



Sound-areas of the Asamayama explosion, December 25, 1910. 



audibility. For instance, in the dynamite explosion which 

 occurred on the Jungfrau railway in 1908, the reports were 

 heard on isolated mountain-summits within the silent zone. 

 In the East London explosion of 191 7, the boom was heard at 

 Ipswich, five miles to the south of the outer sound-area ; pos- 

 sibly also at Uppingham and Lilford in the narrow and more lofty 

 western end of the silent zone. In addition to the sound-waves 



1 F. Omori, "The Eruptions and Earthquakes of the Asamayama," 

 Bulletin of the Earthquake Investigation Committee, vol. vi, 1912, pp. 1-147 ; 

 vol. vii, 1914, pp. 1-215 ; "The Sakura-jima Eruptions and Earthquakes," 

 ibid., vol. viii, 1916, pp. 35-179. 



